HISTORY  OF  CHEMISTRY 


BY 

FRANCIS  P.  VENABLE,  PH.D.,  D.Sc.,  LL.D. 


D.  C.  HEATH  &  CO.,  PUBLISHERS 

BOSTON  NEW   YORK  CHICAGO 


COPYRIGHT,  1922, 
BY  D.  C.  HEATH  &  Co. 

2*2 


PRINTED  IN  U.S.A. 


PREFACE 

The  first  edition  of  this  book  appeared  in  1894.  While 
it  has  passed  through  a  number  of  editions  since,  there  has 
been  no  attempt  to  bring  it  up  to  date  nor  to  revise  it  in 
any  way,  and  although  there  has  been  much  to  preoccupy 
me,  especially  in  other  lines  of  work,  I  recognize  the  fact 
that  there  has  been  no  excuse  for  such  neglect. 

It  has  now  been  entirely  rewritten  on  a  changed  plan 
of  arrangement  and  made  to  cover  the  great  progress  in 
the  science  which  has  taken  place  since  it  first  appeared. 
Some  material  considered  unnecessary  has  been  eliminated 
so  that  it  might  be  kept  within  the  same  compass  that  has 
proved  so  convenient  for  those  who  could  not  devote  to 
the  subject  the  time  required  by  the  larger  treatises. 

FRANCIS  P.  VENABLE 
Chapel  Hill,  N.  G. 
June,  1922 


iii 

4800;K; 


CONTENTS 

PAGE 

CHAPTER  I.    THE  BEGINNINGS 1 

Evolution  of  Science.  —  Industrial  Arts,  Metallurgy.  — 
Minerals  and  Salts.  —  Glass  Making  and  Pottery.  — 
Dyeing  and  Tanning.  —  Soaps  and  Medicaments. 

CHAPTER  II.    EARLY    DEVELOPMENT 8 

Naming  the  Science.  —  Arrangement  of  Facts.  —  Mysti- 
cism. —  Manuscripts  and  Original  Sources.  —  Laws.  — 
Mutability  in  Nature.  —  Theories.  —  Atomic  Theory.  — 
Atoms.  —  Ether.  —  Indivisibility  of  the  Atom.  —  World 
Building.  —  Apparatus. 

CHAPTER  III.    THE  DARK  AGES 19 

The  Old  Order  Overturned.  —  Progress  made  by  the 
Arabians.  —  Transmutation  of  Metals.  —  Geber.  — 
New  Substances. 

CHAPTER  IV.    THE  MIDDLE  AGES 24 

Albertus  Magnus.  —  Roger  Bacon.  —  Changes  in  the 
Sixteenth  Century.  —  Paracelsus.  —  Agricola.  —  Van 
Helmont.  —  Glauber.  —  Rise  of  Theory.  —  Robert 
Boyle.  —  Experiments  upon  Air.  —  Constitution  of 
Matter. 

CHAPTER  V.    THE  CHEMISTRY  OF  COMBUSTION  .  34 
Phlogiston  Theory.  —  Composition  of  Air.  —  Hooke's 
Theory   of   Combustion. 

CHAPTER  VI.    THE  NEW  CHEMISTRY 38 

Analysis.  —  Scheele.  —  Analysis  of  Air.  —  Bperhaave.  — 
Fixity  of  Proportions.  —  Berthollet.  —  Views  as  to 
Affinity.  —  Lavoisier.  —  Character  of  his  Work.  — 
Experiments  on  Combustion.  —  Composition  of  the 
Atmosphere. 


vi  CONTENTS 

PAGE 

CHAPTER  VII.    THE  FOUNDATIONS 48 

Composition  of  Water.  —  Transmutation  of  Water.  — 
The  Atmosphere.  —  Nature  of  Heat  and  Matter.  — 
Theory  as  to  Acids.  —  Elements.  —  Spread  of  the  New 
Chemistry.  —  Black.  —  Priestley.  —  Discovery  of  Oxy- 
gen. —  Study  of  the  Atmosphere.  —  Views  as  to  Com- 
bustion. 

CHAPTER  VIII.    THE  ATOMIC  THEORY 59 

Propositions  of  Lavoisier.  —  Richter.  —  Dalton's  Atomic 
Theory.  —  Constitution  of  Mixed  Gases.  —  Law  of 
Constant  Proportions.  —  Law  of  Multiple  Proportions. 

—  Weights   of   the   Atoms.  —  Dalton's  Rules.  —  Gay- 
Lussac.  —  Law  of  Volumes.  —  Avogadro's  Theory. 

CHAPTER  IX.    THE  ATOMIC  WEIGHTS 70 

The  Standard  for  the  Atomic  Weights.  —  Wollaston's 
Equivalents.  —  Law  of  Specific  Heats.  —  Isomorphism. 

—  Electro-Chemical  Equivalents.  —  Work  of  Dumas.  — 
Vapor  Densities.  —  Gmelia's  Views.  —  Confusion  in  the 
Sixth  Decade.  —  Revisions  of  the  Atomic  Weights.  — 
Clearing  up  the  confusion.  —  Constancy  of  the  Atomic 
Weights. 

CHAPTER  X.    NATURE  OF  THE  ELEMENTARY  ATOM  81 

Prout's  Hypothesis.  —  Views  of  Berzelius.  —  Testing 
the  Hypothesis.  —  Numerical  Relations.  —  Ascending 
Series.  —  Periodic  System.  —  Zero  Group.  —  Contri- 
butions from  Radioactivity.  —  Composite  nature  of  the 
Atom.  —  Evidence  as^to  complexity. 

CHAPTER  XI.    AFFINITY,    THE   ATOMIC    ATTRAC- 
TIVE FORCE 90 

Strength  of  Affinity.  —  Measurement  of  Affinity.  — 
Valence.  —  Evolution  of  the  idea.  —  Organo-Metallic 
Compounds.  —  Polybasic  Acids.  —  Polyatomicity.  — 
Deduction  from  Inorganic  Compounds.  —  Progress 
made. 

CHAPTER  XII.    GROWTH  OF  INORGANIC 

CHEMISTRY 99 

Discovery  of  New  Elements.  —  Humphrey  Davy.  — 
Decomposition  of  the  Alkalis.  —  Composition  of  Muria- 


CONTENTS  Vli 

PAGE 

tic  Acid.  —  New  Theory  of  Acids.  —  Alkalizing  Prin- 
ciple. —  Berzelius.  —  Contributions  of  Berzelius.  — 
Analytical  and  Experimental  Work.  —  Determination  of 
Atomic  Weights.  —  Introduction  of  Symbols.  —  Dualis- 
tic  Theory.  —  Additions  to  list  of  Elements.  —  Mona- 
tomic  Gases.  —  Further  Development  of  Inorganic 
Chemistry. 

CHAPTER  XIII.    THE  DEVELOPMENT  OF  ORGANIC 

CHEMISTRY 115 

Views  of  Lavoisier.  —  Views  of  Berzelius.  —  Isomerism. 

—  Synthesis   of   Urea.  —  Organic   Analysis.  —  Classifi- 
cation of  Organic  Substances.  —  Extension  of  the  Elec- 
tro-Chemical Theory.  —  Extension  of  Radical  Theory. 

—  Benzoic  Acid  Radical.  —  Changes  in  Radical  Theory. 

—  Compound  Radicals. 

CHAPTER  XIV.    FURTHER  THEORIES  AS  TO 

STRUCTURE 126 

Atomic  Theory  confirmed.  —  Substitution  Theory  and 
Overthrow  of  Dualism.  —  Substitution  of  Chlorine  for 
Hydrogen.  —  Trichloracetic  Acid.  —  Unitary  Theory. 

—  Nucleus     Theory.  —  Type     Theory.  —  Homologous 
Series.  —  Application    of    Valence    Theory.  —  Benzene 
Theory.  —  Stereochemistry.  —  Pasteur.  —  Syntheses 
from  Coal  Tar. 

CHAPTER  XV.    PHYSICAL   CHEMISTRY 138 

Law  of  Mass  Action.  —  Electrolytic  Dissociation.  — 
Physical  Properties  of  Solutions.  —  Osmotic  Pressure. 

—  Experiments  of  Van't  Hoff.  —  lonization  Theory.  — 
Colloidal  Chemistry. 

CHAPTER  XVI.    BIOCHEMISTRY "\  .146 

Account  of  its  Development. 

CHAPTER  XVII.    RADIOACTIVITY 150 

The  Discovery.  —  Radium.  —  The  Radiations.  — 
Radioactive  Substances.  —  Disintegration  Theory.  — 
Constitution  of  the  Atom.  —  The  New  Atom  and  its 
Properties.  —  Factors  in  Element  Formation.  —  Iso- 
topes. —  Matter  and  the  Universe. 


HISTOEY   OF   CHEMISTRY 

CHAPTER  I 

THE  BEGINNINGS 

Evolution  of  Science.  —  In  attempting  to  discover 
traces  of  a  science  in  earliest  historic  times  one  must 
first  free  his  mind  of  the  idea  that  he  will  find  it  in  any- 
thing like  the  elaborated  modern  form  in  which  he  knows 
it.  These  natural  sciences  are  the  result  of  a  long  and 
laborious  process  of  evolution.  First  comes  the  gather- 
ing of  facts  and  observations,  and  so  the  beginnings  go 
far  back  of  history  to  the  earliest  representatives  of  the 
race.  The  early  motive  was  the  struggle  to  maintain 
life  and  increase  bodily  comforts,  and  this  motive  has 
not  lost  its  force  in  the  modern  world.  Man  is  a  weapon- 
using  and  tool-making  animal  and  so  gathered  and  fash- 
ioned the  objects  which  best  served  his  purposes.  Com- 
fort demanded  clothing  and  shelter;  therefore,  he  be- 
came weaver,  tanner,  and  builder  of  houses.  His  higher 
nature  developed  the  love  of  beauty  and  so  he  sought 
out  paints  and  dyes;  his  ailments  forced  upon  him  some 
knowledge  of  remedies  and  medicines.  With  the  change 
from  nomad  to  citizen  his  necessities  became  greater 
and  his  inventive  genius  was  stimulated.  Trades  and 
industries  arose  and  with  these  came  specialization  in 
labor  and  formulation  of  knowledge. 

Yet  there  was  nothing  which  could  be  called  science 
and  all  is  still  beyond  recorded  history.  The  beginnings 

1 


2  :  •: 


HISTORY  OF  CHEMISTRY 


described  were  found  wherever  civilization  centered  — 
in  Mesopotamia,  China,  India,  Egypt,  and  European 
Greece.  The  growth  of  knowledge  through  experience, 
or  empiricism,  is  exceedingly  slow.  Yet  a  number  of  in- 
dustrial arts  sprang  up  and  some  were  carried  on  with  a 
high  degree  of  skill.  Artificial  aids  and  labor-saving 
machinery,  such  as  the  blast  furnace  and  potter's  wheel, 
were  called  into  use.  There  were  invented  tools  making 
use  of  physical  laws,  even  though  these  laws  were  not 
recognized  or  understood.  Among  these  were  the 
wedge,  the  lever,  the  screw,  the  wheel.  Improvement 
and  wider  application  of  these  fundamentals  came  with 
growing  understanding  of  principles  involved. 

Industrial  Arts :  Metallurgy.  —  An  outline  of  the 
knowledge  attained  in  some  of  these  arts,  many  of  which 
date  back  to  the  most  remote  antiquity,  may  well  be  con- 
sidered here.  Taking  up  metallurgy  first  we  find  that 
six  metals  were  well  known  —  gold,  silver,  tin,  iron, 
copper,  and  lead.  Homer  mentions  these  six  and  the 
Bif}le  does  also;  so  they  seem  to  have  been  in  use  from 
very  ancient  times.  Mercury  was  afterwards  added 
to  the  list.  The  derivation  of  the  word  metal  is  from 
the  Greek  word  jueraXXaw,  to  search  after,  and  the  noun 
first  meant  or  referred  to  mines.  The  ancients,  espe- 
cially the  Egyptians,  were  very  skillful  workers  in  metals. 
They  made  gold  wire  and  leaf  and  fine  inlaid  work. 
Gold  was  apparently  the  first  known  of  the  metals. 
Its  color,  lustre,  and  malleability,  as  well  as  its  freedom 
from  tarnish  and  corrosion,  attracted  the  attention  of 
the  early  peoples.  Its  rarity  and  value  soon  brought 
it  into  use  as  a  medium  of  exchange,  and  very  early  corns 
have  been  preserved.  Its  occurrence  in  the  free  state 


THE  BEGINNINGS  3 

would  doubtless  account  for  its  being  recognized  and 
used  among  the  first  of  the  metals.  Early  vessels  were 
made  from  it,  as  witness  those  which  have  been  found 
in  ancient  Troy.  It  was  also  used  for  coating  or  plating 
wood  and  other  materials. 

Silver  seems  to  have  become  known  and  to  have  been 
used  at  about  the  same  time  as  gold.  It  also  was  found 
free  and  was  easily  made  ready  for  use.  Then  follow 
copper,  iron,  tin,  and  lead.  The  Egyptians  attributed 
the  discovery  of  the  metals  to  their  sovereigns;  the 
Phoenicians  and  other  peoples  to  their  divinities. 

The  purification  of  gold  and  silver  by  the  cupella- 
tion  process  was  known  before  the  Christian  era,  but 
there  was  no  means  known  for  the  separation  of  gold 
from  silver.  The  alloy  of  the  two  metals,  in  which  enough 
silver  was  present  to  whiten  the  whole,  was  often  found 
and  was  called  electrum,  being  regarded  as  a  distinct 
metal  from  the  others.  Letters  made  of  electrum  a  foot 
or  more  in  height,  which  had  been  fastened  to  the  walls 
of  the  temples,  were  found  in  the  ruins  of  Herculaneum. 
The  oldest  coins  were  made  of  white  or  pale  gold.  After 
a  while  it  was  found  that  this  alloy  could  be  made  arti- 
ficially by  melting  together  three  parts  of  gold  and  one 
of  silver. 

Copper  was  in  use  before  iron  and  was  called  -x.a\K.os 
by  Homer.  From  this  we  get  the  names  for  certain 
copper  minerals,  as  chalcopyrite  and  others.  The  Romans 
obtained  it  first  from  the  island  of  Cyprus  and  called  it 
aes  cyprium,  and  from  this  it  became  cuprum,  a  name 
used  now  in  connection  with  its  salts.  It  was  used  mainly 
in  alloys,  as  with  gold  for  coinage  and  jewelry  and  with 
zinc  as  brass.  Zinc  itself  was  unknown  to  them  but  the 


4  HISTORY  OF  CHEMISTRY 

ore  was  used  along  with  the  copper  in  making  brass. 
Bronze  was  an  alloy  of  copper  and  tin  and  was  known 
also  before  the  method  of  extracting  tin  from  its  ore  had 
been  discovered.  This  was  very  strong,  much  easier  to 
prepare  than  iron,  and  more  readily  worked  into  shape. 
It  was  therefore  a  more  abundant  and  cheaper  material 
and  was  used  for  many  purposes  where  we  use  iron. 
Weapons  and  many  utensils  were  made  from  it.  There  is 
a  tradition  that  the  Egyptians  knew  a  way  of  hardening 
and  tempering  copper  without  alloying  it  and  that  this 
is  one  of  the  so-called  lost  arts. 

Iron  was  known  in  very  early  times.  As  it  rusts  so 
easily,  very  few  early  implements  have  come  down  to 
us.  It  had  to  be  extracted  from  its  ore.  Probably  through 
some  happy  accident  the  method  became  known.  For 
many  centuries  down  into  modern  times  the  art  has 
been  practised  in  India.  A  little  pure  ore  mixed  with 
charcoal  was  heated  by  a  blow-pipe  and  a  small  lump 
of  iron  was  produced.  These  lumps  were  heated  and 
hammered  together  and  a  serviceable  cutlery  steel  ob- 
tained. The  early  Egyptians  understood  how  to  harden 
or  temper  iron  and  quite  possibly  used  such  iron  imple- 
ments in  part  of  the  work  of  constructing  the  pyramids. 
Iron  was  coined  by  the  Greeks  and  in  the  time  of  Homer 
they  used  it  for  axes  and  ploughshares.  The  difficulty 
of  reducing  iron  from  its  ores  on  a  large  scale  would 
account  for  its  not  being  used  more  largely  and  at  an 
earlier  time. 

Tin  was  obtained  from  India  and  Spain  and  after- 
wards from  Britain.  It  was  one  of  the  articles  of  com- 
merce used  in  trade  by  the  Phoenicians.  Mirrors  were 
made  of  it  and  copper  vessels  were  coated  over  with  it. 


THE  BEGINNINGS  5 

Lead  and  tin  seem  to  have  been  regarded  as  varieties 
of  the  same  metal  and  were  called  plumbum  nigrum 
and  plumbum  candidum  respectively.  Pliny  writes  of 
conveying  water  in  lead  pipes  and  Homer  makes  much 
earlier  mention  of  the  metal.  It  came  mainly  from 
Spain  and  Britain.  From  the  former  country  mercury 
also  was  obtained  and  was  used,  as  now,  in  extracting 
gold  from  its  ores.  Native  mercury  was  called  argentum 
vivum  or  quicksilver. 

Minerals  and  Salts.  —  The  two  oxides  of  copper,  as 
they  occur  in  nature,  were  used  in  glass  making;  ver- 
digris was  manufactured  and  put  to  several  uses;  white 
lead  was  used  as  a  cosmetic  by  the  Athenian  ladies  and 
found  further  use  as  a  medicine;  red  lead  was  used  as 
a  paint.  The  native  antimony  sulphide  was  used  to 
paint  the  eyebrows  and  is  still  used  for  that  purpose 
in  the  East  under  the  name  kohl.  Black  oxide  of  man- 
ganese was  used  in  glass  making  for  clearing  up  colored 
or  darkened  glass  and  so  received  the  name  pyrolusite. 
The  native  carbonate  of  zinc  was  used  in  making  brass; 
the  two  sulphides  of  arsenic  were  well-known  pigments. 
According  to  Davy,  the  ancient  Greeks  and  Romans 
used  almost  the  same  colors  as  those  employed  by  Ital- 
ian artists  at  the  period  of  the  revival  of  art  in  Italy. 

Soda  and  potash  were  used  in  washing  and  whitening 
clothes  and  in  saponifying  fats  for  soaps  and  unguents. 
Lime  was  burned  and  mortar  made  from  it,  though  the 
earliest  cementing  materials  seem  to  have  been  pitch  and 
bitumen.  Excellent  hydraulic  cement  was  made  and  used 
by  the  Romans  in  their  great  aqueducts.  Salt  and  salt- 
peter were  used  as  food  preservatives.  Alum  was  used 
in  dyeing.  Vinegar  was  the  only  acid  known. 


6  HISTORY  OF  CHEMISTRY 

Glass  Making  and  Pottery.  —  The  art  of  glass  making 
is  very  old  and  seems  to  have  originated  with  the  Egyp- 
tians. An  account  of  its  accidental  discovery  by  the 
Phoenicians  has  also  been  handed  down.  Certainly  the 
Egyptians  reached  a  high  proficiency  in  making  glass, 
coloring  and  forming  it,  and  also  in  the  production  of 
imitation  precious  stones.  They  were  unable,  however, 
to  produce  clear,  colorless,  and  flawless  glass.  The  seat 
of  the  industry  was  later  transferred  to  Byzantium, 
the  capital  of  the  Eastern  Empire,  and  the  art  of  glass 
making  was  brought  to  Europe  by  the  early  crusaders, 
as  also  a  number  of  other  industries  were  brought  back. 

The  making  of  bricks  and  pottery  must  have  been 
one  of  the  earliest  efforts  of  man  in  the  line  of  manufac- 
ture. The  potter  and  the  potter's  wheel  were  known 
among  all  the  ancient  peoples.  Specimens  of  pottery 
have  been  unearthed  from  the  earliest  ruins.  With  the 
introduction  of  enamels,  glazes,  and  decorations  it  be- 
came an  art,  and  in  this  both  the  Etruscans  and  Egyp- 
tians excelled.  The  Chinese  alone  of  the  early  nations 
knew  how  to  make  porcelain. 

Dyeing  and  Tanning.  —  Dyeing  was  carried  to  great 
perfection.  Many  plant  and  animal  coloring  matters 
were  known.  Mordants  were  used  and  the  effects  pro- 
duced were  very  beautiful.  Paints  were  also  prepared 
and  applied  with  brushes.  The  following  mineral  colors 
were  known  at  the  time  of  Pliny:  White  lead,  red  lead, 
zinc  white,  cinnabar,  smalt,  verdigris,  ochre,  lampblack, 
realgar,  orpiment,  stibnite,  and  the  oxides  of  copper. 

Leather  was  first  tanned  by  means  of  oils  and  later 
with  bark,  very  much  after  the  methods  now  in  use. 
The  hair  was  removed  by  means  of  lime.  Some  leather, 


THE  BEGINNINGS  7 

tanned  centuries  before  the  Christian  era,  has  been  found 
in  modern  times  in  a  state  of  fair  preservation. 

Soaps  and  Medicaments.  —  Soap  was  made  by  mix- 
ing wood  ashes  with  animal  fats,  thus  saponifying  them. 
It  was  used  chiefly  as  a  kind  of  pomatum;  unguents, 
oils,  etc.,  were  rubbed  upon  the  body  in  the  place  of 
soap  as  used  in  modern  times.  Both  hard  and  soft  soap 
were  known.  Burnt  lime  was  often  added  in  its  manu- 
facture. 

Many  substances  were  used  as  medicaments.  Some 
of  these  might  be  called  chemical  preparations,  showing 
an  early  union  between  chemistry  and  pharmacy.  Lead 
plasters  were  made  from  litharge  and  oil;  iron  rust  was 
used  and  also  alum,  soda,  and  bluestone.  Sulphur  was 
employed  as  a  disinfectant  and  also  for  bleaching  pur- 
poses. Mineral  waters  were  used  and  likewise  various 
infusions  from  plants. 

Of  course  all  races,  and  even  the  lower  animals,  had 
in  the  lapse  of  time  discovered  in  plants  and  minerals 
sundry  remedies  for  their  ailing  bodies.  In  the  case  of 
man  the  cures  were  often  brought  about  then  as  now  by 
psychic  suggestion  rather  than  through  the  actual  cura- 
tive properties  of  .the  substances  themselves.  Disease 
was  caused  by  the  presence  of  an  evil  spirit  which  had 
to  be  exorcised  before  health  could  be  restored.  Thus 
Homer  refers  to  the  use  of  sulphur  to  drive  away  the 
evil  spirits.  The  first  chemists,  then,  who  stored  up 
knowledge  of  chemical  substances  might  be  classed  as 
healers,  and  the  earliest  documentary  evidences  were  in 
the  form  of  lists  of  remedies  and  cures.  Such  papyri 
have  been  found  in  early  Egyptian  tombs. 


CHAPTER  II 

EARLY  DEVELOPMENT 

Naming  the  Science. — As  has  been  shown,  chemistry 
early  became  allied  with  so-called  magic  and  witch- 
craft, and  those  who  practised  it  were  usually  feared 
and  held  in  bad  repute.  It  is  probably  this  association 
which  gave  the  name  to  the  science.  The  Greek  word 
XTjMcta  is  manifestly  a  rendering  of  the  Egyptian  name 
chema  or  chemi.  Plutarch  tells  us  that  chemia  was  a 
name  given  Egypt  on  account  of  its  black  soil,  and  that 
this  term  further  meant  the  black  of  the  eye,  symbol- 
izing that  which  was  obscure  or  hidden.  The  Coptic 
word  khems  or  chems  is  closely  related  to  this  and  also 
signifies  obscure,  occult;  and  with  this  is  connected  the 
Arabic  chema,  to  hide.  It  was,  therefore,  the  occult 
or  hidden  science,  the  black  art. 

Arrangement  of  Facts.  —  The  second  stage  in  the 
evolution  of  the  science  is  the  gathering  together  of 
facts  and  observations  and  their  systematic  arranging 
and  recording.  A  beginning  of  this  had  been  made  in 
so  far  as  they  were  related  to  medicine  but  even  there 
few  traces  are  left.  The  conception  of  knowledge  having 
any  value  apart  from  its  immediate  use  in  the  service 
of  man  was  slow  to  arise.  Further,  those  who  sought 
such  knowledge  were  largely  charlatans  and  quacks 
who  had  nothing  to  gain  by  enlightening  their  dupes 
and  feared  prosecution  and  punishment. 

8 


EARLY  DEVELOPMENT  9 

Mysticism.  —  The  earliest  writings  were  lost  or  de- 
stroyed. For  instance,  Diocletian  is  said  to  have  burned 
all  of  the  Egyptian  manuscripts  bearing  on  alchemy 
because,  as  he  said,  these  taught  the  art  of  making  gold 
and  silver,  and  by  destroying  them  he  took  away  their 
power  of  enriching  themselves  and  rebelling  against 
Rome.  Whether  Diocletian  actually  did  this  or  not, 
it  is  certain  that  these  books  of  a  feared  and  prohibited 
art  were  subject  to  many  another  foray,  as  is  evidenced 
by  the  scene  recorded  in  the  Acts  of  the  Apostles:  "  Many 
of  them  which  used  curious  arts  brought  their  books 
together  and  burned  them  before  all  men:  and  they 
counted  the  price  of  them  and  found  it  fifty  thousand 
pieces  of  silver."  Such  scenes  were  often  repeated  in 
the  early  part  of  the  Christian  era. 

The  phrasing  used  in  these  writings  was  purposely 
so  obscure  that  only  the  initiated  were  supposed  to  be 
able  to  understand  them,  and  this  persisted  throughout 
the  period  of  the  alchemists.  It  sufficed  not  merely  to 
cloak  knowledge  but  to  conceal  ignorance. 

Another  piece  of  mysticism  is  seen  in  the  ascription 
of  a  divine  origin  to  their  art.  Thus  Zosimus  the  Panopo- 
lite  claimed  that  the  giants,  sprung  from  the  union  of 
the  angels  with  the  daughters  of  men,  were  taught  all 
that  was  supernatural  and  magical  by  their  fathers  and 
this  wonderful  knowledge  was  recorded  in  a  book  called 
chema.  The  adepts  in  alchemy  were  unanimous,  however, 
in  ascribing  the  foundation  of  their  art  to  Hermes.  The 
name  is  synonymous  with  Toth,  the  god  of  intellect, 
the  patron  of  arts  and  sciences  in  ancient  Egypt.  As 
the  god  of  letters,  all  books  were  dedicated  to  him  and 
he  was  in  one  sense  the  author.  Clement  of  Alexandria 


10  HISTORY  OF  CHEMISTRY 

describes  the  solemn  procession  in  which  these  books 
were  borne  in  the  great  ceremonies.  Tin  and  mercury 
were  set  apart  as  metals  sacred  to  him.  During  the  Mid- 
dle Ages  the  science  was  often  known  under  the  name 
of  the  Hermetic  Art,  and  alchemists  called  themselves 
Hermetic  Philosophers.  To  close  anything  very  securely, 
as  for  instance  to  seal  it  in  a  glass  tube,  is  called 
to  this  day  sealing  it  hermetically.  In  old  times  the 
symbol  of  Hermes  was  affixed  and  it  was  thus  sealed 
with  "  Hermes,  his  seal.'7  The  other  metals  had  their 
patron  deities  also.  Thus  gold  was  sacred  to  the  sun, 
silver  to  the  moon,  and  silver  nitrate  is  still  sold  as  lunar 
caustic.  Copper  was  sacred  to  Venus,  lead  to  Saturn, 
and  iron  to  Mars;  and  one  form  of  iron  oxide  can  be 
bought  on  the  market  still  as  crocus  martis. 

It  was  a  custom  among  the  early  writers  to  ascribe 
their  discoveries,  books,  etc.,  to  fabulous  names  or  an- 
cient heroes  and  gods.  This  had  two  objects,  the  first 
being  to  shield  the  true  author  in  time  of  persecution 
and  the  second  to  gain  a  certain  amount  of  credit  and 
reputation  for  a  discredited  art  by  the  use  of  the  names 
of  such  celebrities  as  Moses,  Solomon,  Alexander,  Cleo- 
patra, etc.  Thus  there  is  a  treatise  entitled  Moses  the 
Prophet  on  Chemical  Composition.  It  is  probable  that 
such  treatises  were  written  in  the  early  centuries  of  the 
Christian  era. 

Manuscripts  and  Original  Sources.  —  This  brings 
us  to  inquire  into  the  existence  of  any  very  early  records. 
No  original  manuscript  of  the  earliest  writers  on  chem- 
istry or  alchemy  has  been  discovered.  Our  knowledge 
must  be  gleaned  from  the  pages  of  those  writing  upon 
other  subjects  or  must  come  from  fragments  handed  down 


EARLY  DEVELOPMENT  11 

through  several  copyists.  The  earliest  manuscripts  known 
are  preserved  in  the  museum  at  Leyden  and  were  found 
at  Thebes  enclosed  in  the  wrappings  of  a  mummy.  They 
are  written  partly  in  Greek  and  partly  in  the  Demotic 
character,  though  they  are  known  as  the  Greek  papyri. 
The  earliest  is  somewhat  fragmentary,  the  beginning 
and  the  end  being  lost.  It  was  written  apparently  about 
the  third  century  of  this  era  and  belonged  to  the  class 
of  books  burned  by  Diocletian.  These  manuscripts 
are  filled  with  magical  formulas,  recipes,  and  descrip- 
tions of  chemical  processes,  together  with  various  forms 
of  apparatus.  Other  later  manuscripts  are  found  in 
various  European  libraries. 

Laws.  —  The  next  stage  to  be  considered  in  the  evolu- 
tion of  the  science  is  the  development  of  laws.  Man, 
with  his  intellectual  gifts,  could  not  rest  content  with 
the  mere  observation  of  facts  and  phenomena.  Their 
orderly  arrangement  so  that  a  certain  uniformity  or 
regularity  and  then  a  controlling  law  could  be  recognized 
was  a  slow  process.  These  laws  were  accepted  and  uti- 
lized as  a  matter  of  every-day  experience  but  their  defi- 
nite statement  came  only  with  comparatively  modern 
science.  A  stone  tossed  in  the  air  returns  to  the  ground 
and  wood  burned  gives  off  certain  gases  along  with 
heat,  but  it  called  for  a  Newton  to  state  the  law  of  grav- 
itation and  not  even  Lavoisier  could  tell  all  the  story 
of  that  burning  and  the  heat.  Some  of  the  early  Greek 
philosophers  guessed  at  the  indestructibility  of  matter, 
but  this  fundamental  conception  played  little  part  in 
their  reasoning. 

Mutability  in  Nature.  —  It  is  easy  to  see  how  confus- 
ing to  the  early  philosophers  were  the  multiform  changes 


12  HISTORY  OF  CHEMISTRY 

in  nature.  Nothing  seemed  lasting  or  stable;  all  was 
subject  to  change.  The  observations  of  one  day  might 
be  quite  overturned  by  those  of  the  morrow.  The  Egyp- 
tians and  other  early  peoples  held  this  view  of  the  chang- 
ing nature  of  all  external  objects  and  the  absence  of 
law  in  these  changes.  Observation  and  experimentation, 
therefore,  appeared  useless.  As  for  the  Greeks,  Socrates 
said  that  the  nature  of  external  objects  could  be  dis- 
covered by  thought  without  observation,  and  the  school 
of  the  Cynics  renounced  all  attempts  at  natural  science. 
It  is  related  that  one  philosopher  put  out  his  eyes  lest 
the  sight  of  these  changes  should  impair  his  thinking. 
Plato  separated  logic,  as  the  knowledge  of  the  immuta- 
ble, from  physics,  the  knowledge  of  the  mutable.  That 
which  was  subject  to  indefinite  change  would  not  repay 
observing  or  recording.  Therefore,  astronomy  and  phys- 
ics could  not  be  conceived  of  as  serious  objects  for  study 
or  contemplation.  There  was  nothing  worth  while  to 
be  learned  from  fields  and  trees  and  stones. 

This  would  seem  to  be  folly  to  the  modern  mind,  but 
it  must  be  acknowledged  that  there  is  danger  from  inac- 
curate observations  and  undigested  facts.  The  safety 
of  the  present  day  lies  in  the  rigid  exaction  of  experi- 
mental proof,  a  means  of  finding  truth  which  these  phi- 
losophers had  scarcely  learned  to  apply.  There  have 
been  and  still  are  deplorable  looseness  of  statement 
and  faulty  logic  on  the  part  of  many,  even  leaders  of 
science.  The  Greek  philosophers  stand  preeminent  as 
the  greatest,  clearest  thinkers  of  all  time. 

Theories.  —  In  spite  of  this  attitude,  the  early  phi- 
losophers made  a  fundamental  start  in  searching  for  the 
underlying  causes  of  the  changes  going  on  in  nature 


EARLY  DEVELOPMENT  13 

and  the  origin  of  the  many  objects  seen  about  them. 
The  theories  which  they  advanced  in  explanation  of 
what  they  observed  form  the  last  and  most  important 
step  in  the  evolution  which  has  been  traced  so  far,  and 
with  these  theories  we  have  truly  the  beginning  of  science 
and  the  casting  off  of  empiricism.  The  first  question 
they  sought  to  solve  was  out  of  what  this  world  was 
made.  While  it  was  possible  that  the  Greeks  got  some 
of  their  ideas  from  the  Egyptians  and  they  might  be 
traced  to  the  sages  of  India  or  the  Far  East,  they  have 
left  us  the  most  abiding  impression  of  their  theories 
and  these,  in  part  at  least,  were  based  on  observation 
and  experiment.  These  philosophers  date  back  to  the 
sixth  century  before  our  era  or  earlier. 

Thus  Thales  of  Miletus,  who  has  been  called  the  first  of 
the  natural  philosophers,  affirmed  that  water  was  the  first 
element  or  principle  and  that  out  of  it  all  things  were 
made.  Thus  water,  on  heating,  is  changed  into  air  and 
from  air  water  comes.  Solids  are  left  when  water  is  boiled 
away.  This  theory  had  its  supporters  even  during  the 
Middle  Ages,  some  of  them  carefully  proving  that  plants 
would  grow  when  fed  with  water  only.  The  theory 
was  not  completely  disproved  until  Lavoisier  showed 
the  fallacy  by  careful  experiment.  When  one  recalls 
its  universal  presence  and  what  trouble  it  causes  the 
expert  chemist  of  to-day  to  avoid  entirely  its  presence 
in  his  experiments,  it  is  easy  to  see  how  natural  the  con- 
clusion was  that  it  was  the  universal,  primal  element. 

Anaximenes  regarded  air  as  the  primal  element;  Hera- 
kleitos,  fire;  Pherekides,  earth.  According  to  Anaxi- 
menes, clouds  were  caused  by  the  condensation  of  air, 
and  rain  by  the  condensation  of  clouds.  Archelaus  said 


14  HISTORY  OF  CHEMISTRY 

that  air,  when  rarefied,  became  fire;  when  condensed, 
water;  and  water,  when  boiled,  became  air.  Of  course, 
the  boiled  natural  water  left  solids.  Empedokles  intro- 
duced the  idea  of  four  distinct  primal  elements  —  earth, 
air,  fire,  and  water  —  which  were  not  interchangeable 
but  formed  all  things  on  being  mixed. 

Atomic  Theory.  —  But  a  further  conception  became 
necessary.  In  this  mixing,  what  is  it  that  is  mixed  or, 
as  we  would  now  express  it,  what  is  the  internal  struc- 
ture of  these  elements?  Are  they  made  up  of  separate 
particles?  If  not,  how  are  they  constituted?  Long  be- 
fore the  time  of  the  Greek  philosophers  the  idea  of  sepa- 
rate particles  seems  to  have  been  conceived  in  India, 
but  for  clear  and  logical  thinking  we  must  again  turn 
to  the  Greeks.  Anaxagoras  of  Klazomene  (500  B.C.) 
was  apparently  the  first  to  formulate  a  theory  approach- 
ing the  atomic.  This  was  more  clearly  expressed  by 
Leukippos  and  extended  by  Demokritos,  who  lived 
450-347  B.C.  He  was  the  founder  of  the  atomistic 
school  and  Aristotle  frequently  cites  his  writings.  As 
was  customary  for  men  of  learning  in  early  times,  De- 
mokritos visited  Egypt,  Chaldea,  and  various  parts  of 
the  East  in  search  of  learning,  and  doubtless  owed  much 
to  the  the  wise  men  of  those  regions. 

Atoms.  —  The  definition  of  an  atom  as  given  by  De- 
mokritos was  almost  as  definite  and  precise  as  that  found 
in  modern  treatises.  The  word  itself  means  that  which 
can  not  be  cut  or  divided.  There  arose  two  schools  of 
philosophers  holding  opposite  views  as  to  the  make-up 
of  the  universe.  The  atomists  maintained  that  it  was 
made  up  of  these  indivisible  particles  separated  by 
empty  spaces  (vacua).  On  the  other  hand,  the  plenists 


EARLY  DEVELOPMENT  15 

contended  for  the  view  that  matter  was  continuous, 
nature  abhorring  a  vacuum.  The  discussion  was  settled 
in  part  by  appeal  to  the  old  argument,  ex  nihilo  nihil. 
If  a  particle  of  matter  were  divided  until  further  sub- 
division was  impossible,  one  must  arrive  at  either  some- 
thing or  nothing.  The  latter  was  impossible,  for  out 
of  nothing,  nothing  can  be  made.  Hence  there  must  be 
an  indivisible  remnant  and  this  should  be  called  an  atom. 

During  the  Middle  Ages  the  word  lost  its  scientific 
significance  and  was  adopted  for  small  subdivisions  of 
various  kinds,  as  of  time  or  music  or  anything  very  small 
and  supposedly  indivisible.  Thus  in  general  the  word 
denoted  a  moment,  a  note,  a  sand  grain,  a  particle  of 
dust,  etc.  Where  in  the  Bible  we  read  that  man  was 
created  out  of  dust  one  can  quite  properly  substitute 
its  synonym,  atom,  and  so  place  it  in  full  accord  with 
the  truth  as  seen  through  man's  study  of  nature. 

Ether.  —  The  vacua  of  the  earlier  philosophers  were 
filled  by  Aristotle  with  his  hypothetical  ether  —  the 
fifth  element  or  quinta  essentia.  This  ether  is  just  as 
essential  for  the  present-day  explanations  of  natural 
phenomena  and  its  existence  is  just  as  evasive  of  abso- 
lute, direct  proof.  Its  invention  at  that  time  is  perhaps 
the  most  marvellous  achievement  of  the  most  profound 
intellect  which  has  devoted  itself  to  science  and  which 
dominated  all  branches  of  science  throughout  the  changes 
of  a  millennium  and  a  half. 

Indivisibility  of  the  Atom.  —  As  to  the  indivisibility 
of  the  atom  in  the  modern  theories,  it  may  be  added  that 
the  compound  nature  of  the  so-called  elemental  atom 
is  well  recognized.  To  the  chemist  this  question  of 
divisibility  or  indivisibility  is  a  matter  of  comparative 


16  HISTORY  OF  CHEMISTRY 

indifference.  It  suffices  that  in  all  the  various  reac- 
tions of  the  laboratory  the  atom  retains  its  individual 
character  and  may  be  regarded  as  indivisible  so  far  as 
the  usual  manipulations  are  concerned. 

World  Building.  —  Granted  that  the  world  was  made 
of  atoms,  how  was  it  put  together?  This  problem  also 
was  faced  and  discussed  by  the  Greek  philosophers. 
It  must  be  borne  in  mind  that  the  modern  meaning 
was  not  attached  to  the  word  element  in  early  times 
but  rather  these  were  thought  of  as  certain  principles  or 
essences  which  were  endowed  with  diverse  properties. 
Thus  fire  was  warm  and  dry;  air  was  warm  and  moist; 
water  moist  and  cold;  earth  cold  and  dry.  By  mixing 
these  elements  various  combinations  and  interchanges 
of  properties  were  thought  to  be  possible. 

According  to  Anaxagoras,  there  was  at  first  a  mixing 
of  these  particles  of  matter,  the  primal  constituents,  in 
infinite  disorder  or  chaos.  The  act  of  creation  was  in 
the  orderly  arranging  of  these  by  a  designing  intelligence, 
vovs.  These  particles  were  like  the  masses  which 
they  produced  when  brought  together  and  were  named 
homoeomeries  or  like  parts,  and  hence  were  not  the  atoms 
of  atomists  but  corresponded  to  the  molecules  of  the 
present  day.  The  act  of  creation  came  about  through 
a  vortical  motion  which  would  separate  these  mole- 
cules and  bring  together  those  alike  in  size  and  specific 
gravity,  thus  building  up  the  various  substances  known 
to  us.  This  idea,  of  course,  is  drawn  from  the  simple 
^experiment  of  giving  a  rotary  motion  to  a  vessel  con- 
taining finely-divided  substances  of  different  densities. 

The  atomists  sought  to  do  away  with  the  necessity 
for  a  designing  intelligence  by  conceiving  the  indivisible 


EARLY  DEVELOPMENT  17 

atoms  or  molecules,  which  were  said  to  possess  rapid 
circular  motion,  as  falling  together.  These  atoms  were 
invisible,  indivisible,  solid,  impenetrable,  and  unalterable, 
possessing  no  other  properties  except  size,  shape,  and 
weight.  They  were  influenced  by  necessity  or  fate, 
avajKrj.  The  meaning  here  seems  to  be  covered  by 
our  word  law.  In  falling  they  had  an  oblique  motion 
which  caused  atoms  of  like  shape  to  collide  and  gather 
into  masses.  Of  course,  a  vacuum  or  void  was  an  es- 
sential for  this  theory.  Aristotle  pointed  out  that  there 
could  be  no  up  nor  down  in  mere  space,  no  place  to  fall 
from  and  none  to  fall  to,  and  hence  falling  was  out  of 
the  question.  If  there  were  objects  falling,  they  must 
fall  in  parallel  lines  and  could  never  meet.  So  Epicurus 
coined  a  new  word  to  convey  a  new  thought.  This  word 
meant  inclination.  This  brought  like  particles  together 
and  in  this  we  have  the  first  suggestion  of  affinity.  This 
idea  was  held  also  by  the  Hindus,  who  said,  "There 
is  a  strong  propensity  which  dances  through  every  atom 
and  attracts  the  minutest  particle  to  some  peculiar 
object."  This  " propensity,"  however,  they  manifestly 
confused  or  identified  with  gravity.  Aristotle  regarded 
the  moving  ether  as  the  motive  principle.  Long  cen- 
turies afterwards  Helmholtz  proved  mathematically  that 
whatever  the  original  motion  was  it  could  not  have  been 
set  up  except  through  the  application  of  some  exterior 
force. 

Thus  in  these  very  early  times  the  foundations  of 
experience  —  gathered  facts,  experimental  testing,  and 
workable  hypotheses  —  were  laid  for  the  development 
of  a  true  science  with  its  attendant  benefits  to  civiliza- 
tion. But  this  decided  progress  was  all  but  blotted  out 


18  HISTORY  OF  CHEMISTRY 

in  the  grave  political  changes  which  took  place  with 
the  fall  of  the  Roman  Empire. 

Apparatus.  —  It  is  of  interest  to  inquire  by  what 
means  experimentation  was  carried  on,  and  under  what 
conditions,  in  these  early  centuries  and  for  a  number 
of  those  following.  Some  information  as  to  this  may 
be  derived  from  the  Greek  papyri.  These  contain  many 
drawings  of  alembics  and  other  forms  of  apparatus 
which  may  of  course  have  been  later  inventions  if  the 
great  age  of  these  papyri  is  disproved.  The  processes 
used  were  those  requiring  fire  —  dry  methods  rather 
than  wet.  Crucibles,  furnaces,  etc.,  abound  therefore. 
There  is  a  treatise  by  Zosimus  on  instruments  and  fur- 
naces in  which  he  claims  to  describe  the  various  appli- 
ances he  saw  in  the  ancient  temple  at  Memphis.  These 
were  made  of  gold  or  bronze  or  clay.  The  alembic  was 
a  crude  form  of  still  and  came  from  the  Alexandrian  pe- 
riod. The  water-bath,  or  bain-marie  as  it  is  still  called 
by  the  French,  was  said  to  have  been  invented  at  a  very 
early  period  by  Mary  the  Jewess.  The  blow-pipe  and 
bellows  both  figured  among  these  drawings  as  well  as 
on  very  early  Egyptian  and  other  monuments.  The 
use  of  glass  for  apparatus  came  much  later.  Jars  and 
bowls  of  clay  and  other  ware  about  complete  the  list. 
An  investigator  of  the  present  time  limited  to  such  scant 
.equipment  would  indeed  be  helpless. 


CHAPTER  III 

THE  DARK  AGES 

The  Old  Order  Overturned.  —  With  the  overturning 
of  the  Eastern  Empire  by  the  Arabians  and  the  Western 
Empire  by  the  Goths  and  Vandals  one  of  the  world's 
greatest  civilizations,  already  decadent,  was  almost 
wiped  out.  In  these  troubled  centuries  of  the  Dark  Ages 
few  devoted  themselves  to  literature,  art,  or  science. 
The  creative  faculty  was  blunted  and  no  great  artist 
or  philosopher  was  produced.  But  happily  the  light  was 
not  altogether  extinguished.  The  useful  arts  were  re- 
tained and  Greek  learning,  with  its  budding  science, 
was  transferred  to  Arabia  and  Persia.  About  the  middle 
of  the  eighth  century  there  was  established  at  Bagdad 
an  academy  or  university  which  was  visited  by  thou- 
sands of  those  seeking  instruction.  Hospitals  and  labora- 
tories were  built  and  experimental  science  made  some 
progress.  Ancient  books  were  collected  and  every  scrap 
that  could  add  to  the  store  of  knowledge  was  preserved. 
This  University  of  Bagdad  flourished  for  several  centu- 
ries and  scholars  came  to  it  from  distant  parts  of  the 
world. 

This  love  of  learning  extended  to  the  western  pos- 
sessions of  the  Arabians.  Universities  were  founded 
in  northern  Africa  and  Spain.  The  University  of  Cor- 
dova, for  instance,  held  a  high  reputation  and  was  at- 
tended by  many  Christian  students.  Its  library  was 

19 


20  HISTORY  OF  CHEMISTRY 

said  to  contain  280,000  volumes.  But  a  volume  in  those 
days  often  contained  only  a  single  stanza  of  a  poem  or 
a  single  chapter  of  a  book. 

Progress  Made  by  the  Arabians.  —  With  all  their 
zeal  for  learning  and  for  hoarding  ancient  books  and 
the  writing  of  new  ones,  the  Arabs  made  little  prog- 
ress in  science.  Centuries  passed  with  but  slight  ad- 
ditions to  what  was  already  known.  Nor  did  they  give 
evidence  of  the  clear  thinking,  logic,  and  vision  of  the 
Greeks.  There  was  little  worthy  effort  at  explaining 
phenomena  or  advance  in  theory.  Their  chief  interest 
in  chemistry  lay  in  finding  or  preparing  new  remedies 
to  be  applied  in  the  art  of  healing.  This  included  the 
search  for  the  philosophers'  stone,  which  at  first  was  a 
remedial  agent  or  universal  medicine.  Later  it  became 
a  supposed  means  of  turning  base  metals  (as  lead)  into 
gold.  It  was  to  this  last  object  that  the  time  and  energy 
of  the  alchemists  were  gradually  diverted. 

Transmutation  of  the  Metals.  —  When  it  is  recalled 
that  the  metals  were  not  in  themselves  elements  to  the 
ancients  but  a  "  bundle  of  properties,"  it  is  easy  to  see 
how  the  idea  arose  that  one  might  take  a  common  and 
dull  or,  as  they  considered  it,  a  diseased  metal  and  pu- 
rify or  change  it  into  one  free  from  corruption,  beauti- 
ful and  valuable  like  gold.  This  delusion  was  a  very 
early  one  and  did  much  to  divert  the  course  of  experi- 
mental work  from  its  true  object,  the  search  after  truth, 
to  the  vain  chase  of  a  will-o'-the-wisp.  The  tenacious 
hold  of  this  delusion  is  shown  by  the  fact  that  there  was 
an  alchemical  society  in  France  in  the  latter  part  of  the 
nineteenth  century,  as  well  as  alchemists  in  America, 
still  trying  to  transmute  lead  into  gold. 


THE  DARK  AGES  21 

The  dream  of  transmutation  was  not  altogether  base- 
less. There  was  in  a  way  experimental  proof.  Much 
of  the  lead  contains  gold  and  on  prolonged  treatment 
the  lead  disappears  and  gold  remains.  When  bright 
iron  is  dipped  into  a  solution  of  bluestone  it  is  appar- 
ently changed  into  copper,  for  the  iron  disappears  and 
copper  takes  its  place.  In  a  book  attributed  to  an  Ara- 
bian alchemist  of  the  eight  century  called  Geber  we  read: 
"In  copper  mines  we  see  a  certain  water  which  flows 
out  and  carries  with  it  thin  scales  of  copper  which  by  a 
long-continued  course  it  washes  and  cleanses.  But  after 
such  water  ceases  to  flow,  we  find  these  thin  scales  with 
the  dry  sand  in  three  years  to  be  digested  with  the  heat 
of  the  sun;  and  among  these  scales  the  purest  gold  is 
found;  therefore,  we  judge  those  scales  were  cleansed 
by  the  benefit  of  the  water  but  were  equally  digested 
by  the  heat  of  the  sun,  in  the  dryness  of  the  sand  and  so 
brought  to  equality."  Very  plausible  reasoning  from 
defective  premises,  as  Thomson  observes. 

Geber.  —  Geber  considered  all  metals  to  be  compounds 
of  mercury  and  sulphur  in  varying  proportions,  an  opin- 
ion which  he  said  he  derived  from  the  ancients  and  which 
was  handed  down  with  variations  through  the  Middle 
Ages.  His  observations  on  sulphur  show  the  advances 
made  and  the  limitations  of  the  time.  "Sulphur,"  he 
writes/'  is  a  substance,  homogeneous  and  of  a  very  strong 
composition.  Although  it  is  a  fatty  substance,  it  is  not 
possible  to  distil  its  oil  from  it.  It  is  lost  on  calcining. 
It  is  volatile  like  a  spirit.  Every  metal  calcined  with 
sulphur  augments  its  weight  in  a  palpable  manner. 
All  the  metals  can  be  combined  with  this  body  except 
gold,  which  combines  with  it  with  difficulty.  Mercury 


22  HISTORY  OF  CHEMISTRY 

produces  with  sulphur  by  way  of  sublimation  cinna- 
bar. Sulphur  generally  blackens  the  metals.  It  does 
not  change  mercury  into  gold  nor  into  silver  as  has  been 
imagined  by  some  philosophers." 

Glass  was  by  this  time  included  in  the  materials  used 
for  apparatus  and  the  process  of  distillation  was  prac- 
ticed. The  product  was  called  a  spirit,  as  spirit  of  wine, 
etc.  Geber  understood  the  purification  of  substances 
by  crystallization,  solution,  and  filtration.  The  latter 
process  was  known  as  distillation  through  a  filter.  The 
majority  of  the  processes  in  use  up  to  the  eighteenth 
century  were  known  to  him. 

New  Substances.  —  The  alkaline  substances  were 
known  at  the  time  of  Geber  and  caustic  soda  was  pre- 
pared. Saltpeter  and  sal  ammoniac  or  ammonium  chlo- 
ride were  also  known,  as  well  as  the  mineral  acids,  nitric, 
sulphuric,  and  aqua  regia.  These  were  used  as  solvents 
and  thus  the  wet  processes  of  modern  chemistry  began 
to  substitute  the  dry  processes  of  the  furnaces.  Various 
sulphates,  or  vitriols  as  they  were  called,  were  spoken  of 
and  also  borax  and  purified  common  salt.  Certain  com- 
pounds of  mercury,  as  corrosive  sublimate  and  the  red 
oxide,  were  also  used.  As  an  illustration  of  these  proc- 
esses, we  may  take  the  method  of  preparing  silver  ni- 
trate which  Geber  discovered:  "Dissolve  silver  calcined 
in  solutive  water  (nitric  acid);  which  being  done,  heat 
it  in  a  phial  with  a  long  neck,  the  orifice  of  which  must 
be  left  unstopped,  for  one  day  only,  until  a  third  part 
of  the  water  be  consumed.  This  being  effected,  set  it 
with  its  vessel  in  a  cold  place  and  then  it  is  converted 
into  small  fusible  stones  like  crystal." 

Further  addition  to  knowledge  was  very  limited  until 


THE  DARK  AGES  23 

the  thirteenth  and  fourteenth  centuries.  The  decadence 
of  Moorish  power  in  Europe  was  rapid.  The  Arabs  were 
driven  from  Spain,  and  Bagdad  was  conquered  by  the 
Mongols.  Still  for  some  centuries  the  influence  of  Arabic 
thought  was  great.  Their  writings  were  translated  into 
Latin  and  other  languages  and  formed  the  chief  treasure 
of  medical  and  scientific  workers,  and  their  modes  of 
thought  and  work  were  often  imitated  by  their  monkish 
successors.  Schools  and  universities  were  established 
at  Montpellier,  Paris,  Naples,  Padua,  and  other  places, 
and  the  center  of  learning  shifted  westward  and  north- 
ward. 


CHAPTER  IV 

THE   MIDDLE  AGES 

During  the  previous  centuries  of  intellectual  steril- 
ity in  Europe  the  monks  had  been  the  only  conserva- 
tors of  books  and  scientific  works  —  a  dead  treasure 
in  their  hands.  These  orders  began  to  awaken  to  intel- 
lectual life  and  to  labor  for  the  spread  of  knowledge. 
The  crusaders  brought  various  industries  to  Europe 
from  the  East.  The  gold-making  craze  spread  and  there 
was  much  talk  of  magic.  These  met  with  inquisito- 
rial opposition  on  the  part  of  the  church,  which  indeed 
held  a  close  control  over  all  progress  in  knowledge  or 
introduction  of  new  ideas.  The  only  noted  scientific 
workers  of  the  early  part  of  this  period  came  from  the 
monkish  orders. 

Albertus  Magnus  (1193-1280). —  Thus  Albertus  Mag- 
nus was  Bishop  of  Regensburg.  His  lectures  were  at- 
tended by  thousands  of  students  and  he  wrote  a  number 
of  books.  He  introduced  the  word  affinity  to  designate 
the  cause  of  the  combination  of  the  metals  with  sulphur. 

Roger  Bacon  (1214-1294).  —  Roger  Bacon  was  the 
most  remarkable  man  of  this  time.  He  was  a  Francis- 
can friar  in  England  and  was  persecuted  for  his  alleged 
dealing  with  magic,  spending  some  ten  years  in  prison, 
though  he  had  written  a  book  to  prove  that  there  could 
be  no  such  thing  as  magic.  He  was  an  astronomer, 
mathematician,  physicist,  and  alchemist.  He  was  the 

24 


THE  MIDDLE  AGES  25 

first  to  draw  attention  to  the  error  in  the  Julian  cal- 
endar. It  was  his  success  as  a  mechanic  in  the  produc- 
tion of  several  automata  which  brought  him  the  repu- 
tation of  being  in  league  with  the  devil.  He  seems  to 
have  known  how  to  make  gunpowder  and  it  was  first  used 
by  the  English  at  the  battle  of  Crecy  some  fifty  years 
after  his  death.  He  is  reputed  to  have  been  the  inventor 
of  the  telescope,  camera  obscura,  and  burning  lenses.  He 
subjected  organic  substances  to  dry  distillation  and  noted 
the  inflammable  gases  given  off.  Some  one  during  this 
period  by  distillation  of  bones  obtained  what  was  called 
spirit  of  hartshorn  and  thus  ammonia  was  discovered. 
Also  wine  was  distilled  and  spirit  of  wine  or  alcohol 
obtained.  These  were  about  all  of  the  practical  gains 
in  the  three  centuries  preceding  the  sixteenth. 

Changes  in  the  16th  Century.  —  In  the  sixteenth  cen- 
tury began  a  period  of  restless  adventure  and  discovery, 
together  with  a  throwing  off  of  the  cramping  bonds  of 
authority.  Just  before  the  dawn  of  the  century  America 
was  discovered  and  men  were  exploring  its  wilds.  The 
discoveries  of  Copernicus  as  to  the  stellar  system  and 
the  Reformation  of  Luther  fall  in  this  age.  The  art  of 
printing  was  developed  by  Gutenberg.  Books  became 
more  plentiful  and  about  eighty  universities  in  Europe 
were  giving  a  meagre  training  to  thousands  of  students. 
There  was  a  tendency  to  unite  chemistry  and  medicine. 
Life  processes  began  to  be  accounted  for  on  chemical 
grounds,  and  medicine  was  in  a  measure  a  branch  of 
applied  chemistry  and  then  began  to  be  looked  upon 
as  the  true  aim  and  end  of  chemistry.  In  consequence 
laboratory  work  was  more  carefully  carried  out  and  new 
compounds  were  discovered.  A  new  object  and  zest  were 


26  HISTORY  OF  CHEMISTRY 

given  to  the  study  and  chemistry  became  the  pursuit 
of  trained  scholars. 

Paracelsus  (1493-1541).  —  One  of  the  noted  men  of 
this  century  was  Paracelsus.  He  taught  at  the  Uni- 
versity of  Basel,  covering  the  subjects  of  medicine,  chem- 
istry, and  pharmacy.  His  great  service  lay  in  breaking 
away  from  the  ancient  authorities,  such  as  Galen,  Hip- 
pocrates, and  Aristotle,  insisting  that  instruction  should 
be  given  and  books  written  in  the  language  of  the  people 
so  as  to  be  easily  intelligible  to  them,  and  stressing  the 
importance  of  gathering  knowledge  through  experiment 
and  from  every  first-hand  source.  As  a  physician,  he 
was  skillful  and  successful  and  substituted  for  the  old 
theory  of  disease  (that  it  came  from  excess  in  either  bile, 
phlegm,  or  blood)  a  new  one  that  each  disease  has  its 
own  definite  cause  and  sequences  and  must  be  antago- 
nized by  specific  remedies.  This  marked  the  inaugura- 
tion of  the  modern  method  of  antagonizing  disease. 

As  a  chemist  he  added  much  to  the  previously  known 
analytical  methods  and  the  partial  discovery  of  hydrogen 
is  accredited  to  him,  though  its  distinctive  separation 
and  identification  were  lacking.  He  laid  the  foundation 
for  a  classification  of  the  metals  which  lasted  for  several 
generations  and  he  was  largely  instrumental  in  turning 
chemistry  from  wasteful  aims  into  a  most  useful  adjunct 
to  medicine.  Pharmacy  as  a  distinct  profession  and  ob- 
ject of  study  was  largely  founded  by  him  and  he  intro- 
duced many  new  and  valuable  remedies.  Mercurial 
preparations,  lead  compounds,  iron  salts,  arsenic  for 
skin  diseases,  milk  of  sulphur,  bluestone,  and  others 
might  be  mentioned.  Various  plant  remedies  had  been 
in  use  as  decoctions  or  simply  sweetened  with  sugar. 


THE  MIDDLE  AGES  27 

He  began  the  search  after  their  active  principles  and 
brought  them  into  use  as  tinctures,  essences,  and  extracts. 
Tincture  of  opium,  for  instance,  was  first  used  by  him 
and  given  its  present  name  laudanum. 

Agricola  (1494-1555).  —  Contemporaneous  with  Para- 
celsus but  forming  a  strong  contrast  to  him  was  the  tech- 
nical chemist,  Agricola.  He  was  born  in  Germany  and 
studied  at  Leipsic,  and  was  the  first  and  for  a  long  time 
the  only  one  to  devote  his  scientific  knowledge  to  the 
improvement  of  metallurgy  and  the  industrial  arts.  His 
chief  work  is  called  De  Re  Metallica  and  is  a  connected 
treatise  on  metallurgy.  This  book  went  through  many 
editions  and  was  for  a  long  time  considered  an  authority 
on  the  subject,  substituting  scientific  theories  for  the 
persistent  ancient  beliefs  that  metals  grew  in  the  mines 
in  some  such  way  as  vegetables  grew  in  the  surface  soil, 
that  if  a  mine  were  closed  and  allowed  to  stand  the  metal 
would  grow  again,  and  that  one  metal  might  be  made 
from  another.  In  his  book  is  given  a  clear  account  of 
the  condition  of  the  various  industries  of  his  day  and  the 
different  methods  and  operations  then  in  use.  Agricola 
was  a  physician  as  well  as  technical  chemist  but  he  did 
not  attribute  disease  and  growth  to  the  metals. 

Van  Helmont  (1577-1644).  — Two  more  of  these 
physician-chemists  deserve  mention,  both  belonging  to 
the  seventeenth  century.  The  first  was  Van  Helmont, 
a  Belgian,  who  studied  at  the  University  of  Louvain. 
Most  of  his  life  was  spent  at  work  in  his  private  laboratory 
and  from  this  time  on  we  find  that  in  such  laboratories 
most  of  the  real  progress  was  made.  He  took  up  the 
old-world  theory  that  water  was  the  primal  element  and 
in  support  of  it  advanced  many  ingenious  arguments 


28  HISTORY  OF  CHEMISTRY 

from  plants  and  animals.  He  performed  the  famous 
experiment  of  the  willow  and  it  is  the  most  plausible  among 
his  experiments  adduced  as  proofs  of  his  theory. 

A  large  earthen  vessel  was  rilled  with  two  hundred 
pounds  of  dried  earth  and  a  willow  weighing  five  pounds 
was  planted  in  it.  This  was  duly  watered  with  rain  and 
distilled  water.  After  five  years  the  willow  was  pulled 
up  and  found  to  weigh  one  hundred  and  sixty-nine  pounds 
and  four  ounces.  The  earth  had  decreased  two  ounces 
in  weight.  Thus,  according  to  Van  Helmont's  reasoning, 
one  hundred  and  sixty-four  pounds  of  root,  bark,  leaves, 
etc.,  were  produced  from  water  alone.  Fish  also,  he 
said,  live  on  water  and  yet  contain  all  the  peculiar  animal 
substances.  These  are  then  made  from  water. 

He  introduced  the  term  gas  to  distinguish  water  vapor 
and  other  elastic  fluids  from  air  and  was  the  first  to  study 
these  substances  systematically.  The  vapor  coming  from 
fermenting  substances,  or  carbon  dioxide,  he  called  gas 
sylvestre.  He  divided  gases  into  those  which  were  in- 
flammable and  those  which  were  not.  As  he  was  ignorant 
of  any  method  of  collecting  and  separating  them,  his 
knowledge  was  very  imperfect.  He  believed  in  curing 
diseases  by  dietetics,  by  working  on  the  imagination, 
use  of  incantations,  etc.  Still  he  made  use  of  chemical 
preparations  and  greatly  advanced  them  in  popular 
favor.  At  the  same  time  he  was  an  enthusiastic  mystic, 
believing  in  the  transmutation  of  metals  and  hi  magic. 
Mice,  he  thought,  could  be  made  by  placing  a  soiled  shirt 
with  some  flour  in  a  barrel.  It  may  be  safely  stated  that 
at  least  this  would  be  one  way  of  collecting  them. 

Glauber  (1604-1668).  —  A  more  distinguished  name  is 
that  of  Glauber,  a  German,  whose  skill  was  devoted  to 


THE  MIDDLE  AGES  29 

increasing  the  knowledge  of  chemical  substances.  He  dis- 
covered and  introduced  many  new  chemical  preparations. 
Purer  and  stronger  hydrochloric  and  nitric  acids  were 
prepared  by  him.  He  prepared  sodium  sulphate,  to  which 
he  ascribed  remarkable  curative  powers,  calling  it  sal 
mirabile.  It  has  for  a  long  time  been  known  as  Glauber's 
salt.  Various  other  sulphates  and  chlorides  were  pre- 
pared by  him.  He  used  the  method  of  double  decom- 
position in  his  preparations  and  thus  described  it:  "Aqua 
regia  which  has  taken  gold  into  solution  kills  the  salt 
of  tartar  (potash)  of  the  liquor  of  flints  (silicate  of  potash) 
in  such  way  as  to  cause  it  to  abandon  the  silica,  and  in 
exchange  the  salt  of  tartar  paralyzes  the  action  of  the 
aqua  regia  in  such  way  as  to  make  it  let  go  the  gold  which 
it  had  dissolved.  It  is  thus  that  the  silica  and  gold  are 
both  deprived  of  their  solvents.  The  precipitate  is  com- 
posed, then,  at  the  same  time  of  the  gold  and  of  the  silica, 
the  weights  of  which  together  represent  that  of  the  gold 
and  of  the  silica  originally  employed."  His  appeal  to 
the  balance  for  accuracy  and  as  confirming  his  theory  is 
noteworthy. 

Two  mistakes  were  made  by  these  physicians  and  iatro- 
chemists,  as  they  were  called.  They  attempted  to  ex- 
plain on  chemical  principles  all  the  changes  and  processes 
going  on  in  the  body.  This  was  certainly  not  possible 
with  the  deficient  knowledge  of  the  day.  To  Van  Helmont, 
for  instance,  disease  consisted  in  the  excess  or  preponder- 
ance of  base  or  acid  in  the  body  juices.  Secondly,  too 
narrow  a  limit  was  set  to  chemistry.  It  was  destined  to 
fill  a  much  larger  sphere  than  that  of  an  adjunct  to  any 
other  science. 

The  Rise  of  Theory.  —  The  science  did  not  remain 


30  HISTORY  OF  CHEMISTRY 

long  in  this  subordinate  position.  It  so  grew  in  extent 
and  importance  that  it  was  able  to  burst  the  bonds  of 
too  close  an  alliance  with  medicine  and  to  take  for  its 
field  the  study  of  the  combinations  and  decompositions 
of  all  known  substances.  The  inductive  philosophy  of 
Francis  Bacon  began  to  have  effect  and  chemistry  as- 
sumed its  place  among  the  sciences.  Its  study  was  no 
longer  obscured  by  gold-hunting  nor  limited  to  the  prep- 
aration of  medicines.  There  came  a  period  of  qualitative 
chemistry,  a  step  toward  the  higher  quantitative  work 
and  a  great  step  forward  from  the  haphazard  chemistry 
of  the  past.  There  are  dangers  in  relying  upon  quali- 
tative tests  alone  and  mistakes  were  made.  For  a  while 
the  guiding  principle  seems  to  have  been  the  old  saying 
that  similar  appearances  are  due  to  similar  causes,  a 
saying  which  has  much  plausibility  and  yet  might  lead 
to  error.  Minerals  were  analyzed  and  new  substances 
discovered.  Some  synthetic  work  was  done  and  new 
compounds  formed.  There  was  a  growing  desire  to  know 
something  of  the  underlying  causes,  to  understand  better 
the  phenomena  observed,  and  to  find  explanations  for 
them.  Processes  in  the  laboratory  became  more  frequently 
those  of  the  "wet  way"  where  solutions  were  concerned. 
To  insure  accuracy  and  assist  judgment  more  frequent 
use  was  made  of  the  balance  and  there  was  a  return  to 
logic  and  philosophy  as  in  the  time  of  the  Greeks.  And 
so  the  progress  made  in  the  seventeenth  century  far 
exceeded  that  of  all  the  previous  centuries. 

Robert  Boyle  (1626-1691).  —  First  amdng  those  to 
pursue  the  study  of  chemistry  from  a  noble  desire  for 
a  deeper  insight  into  the  workings  of  nature  was  Robert 
Boyle.  He  was  born  in  Ireland,  lived  at  Oxford,  and  aided 


THE  MIDDLE  AGES  31 

in  founding  the  Royal  Society  of  England.  He  antago- 
nized the  alchemists,  except  in  respect  to  a  belief  in  the 
possible  transmutation  of  the  metals,  and  also  contended 
with  the  views  of  Van  Helmont,  though  he  agreed  that 
one  must  look  to  chemistry  for  the  solution  of  the  greatest 
problems  of  medicine.  He  was  the  first  to  apply  Bacon's 
inductive  method  to  the  science  and  maintained  that 
experiment  alone  was  the  proper  basis  for  theory  and  that 
all  theories  must  be  tested  by  experiment.  Before  at- 
tempting any  theorizing  as  to  explanations  he  went  to 
work  to  correct  the  faulty  experiments  and  imperfect 
observations  of  the  past  and  thus  to  clear  the  path  for 
an  understanding  of  the  phenomena. 

Experiments  upon  Air.  —  Boyle's  experiments  were 
largely  upon  air  and  water,  choosing  two  of  the  common- 
est and  yet  most  instructive  substances  in  nature.  The 
knowledge  of  the  first,  physically  and  chemically,  was 
greatly  advanced  by  him.  He  made  use  of  an  improved 
air-pump  and  examined  the  behavior  of  different  sub- 
stances in  a  vacuum.  He  enunciated  the  law  of  pres- 
sure for  gases,  namely,  that  the  volume  of  a  gas  varies 
inversely  as  the  pressure.  This  is  still  known  as  Boyle's 
Law.  Experiments  were  carried  out  also  as  to  the 
height,  weight,  and  density  of  the  atmosphere.  Further- 
more, he  showed  that  something  in  the  air  was  consumed 
by  breathing  or  by  the  burning  of  a  substance  in  it.  This 
was,  of  course,  only  a  verification  of  observations  made 
long  before.  He  proved  that  an  increase  in  weight  was 
caused  by  calcination  and  that  the  calx  was  specifically 
lighter  than  the  original  metal.  The  calcination  of  such 
a  substance  as  lead,  he  showed,  consumed  air.  It  is 
strange  how  near  his  experiments  brought  him  to  impor- 


32  HISTORY  OF  CHEMISTRY 

tant  truths.  But  he  was  not  always  happy  in  the  inter- 
pretation of  his  results.  He  could  see  many  faults  in  the 
theories  of  the  times  but  seldom  saw  his  way  clear  to 
establishing  a  theory  of  his  own. 

Constitution  of  Matter.  —  In  studying  the  nature  of 
the  various  substances  known  to  him  Boyle  devised  a 
system  of  qualitative  analysis,  arranging  these  substances 
into  classes  and  groups.  Vegetable  coloring  matters  were 
used  by  him  as  indicators  for  acids  and  bases.  Regular 
reagents  were  introduced  by  him  with  directions  for 
their  use.  Many  of  his  teats  we  make  use  of  at  the  present 
day  as,  for  instance,  ammonia  was  driven  out  of  its  com- 
pounds by  lime  or  caustic  potash  and  tested  for  by  its 
fuming  with  hydrochloric  acid.  His  ideas  as  to  the  con- 
stitution of  matter  were  much  like  those  of  the  present. 
He  considered  all  bodies  to  consist  of  very  small  particles 
and  believed  that  the  union  of  these  particles  gave  com- 
pounds. Decomposition  was  impossible  until  the  attrac- 
tion between  the  particles  had  been  overcome.  Accord- 
ing to  this  hypothesis,  the  differences  between  bodies 
were  due  to  the  inequalities  in  the  form,  structure,  and 
movement  of  the  particles.  In  his  opinion  one  or  two 
primal  elements  would  suffice  to  explain  all  the  varieties 
of  substances  in  nature.  This  comes  rather  close  to  the 
hydrogen-helium  hypothesis  of  the  present.  And  yet 
when  he  came  to  apply  his  hypothesis  his  limitations 
became  very  apparent.  The  particles  of  water,  he  sup- 
posed, might  under  certain  conditions  be  so  grouped  and 
set  in  motion  as  to  form  the  substance  which  we  know  as 
air.  It  is  easy  to  see  that  all  through  the  ages  one  of  the 
great  puzzles  set  for  thinking  men  has  been  the  invisible 
atmosphere  surrounding  us,  forming  and  buoying  up  its 


THE  MIDDLE  AGES  33 

cloud  masses  and  pouring  down  its  floods  of  water,  hail, 
or  snow. 

In  defining  a  chemical  compound  as  one  formed  by  the 
union  of  two  or  more  components  which  lose  their  prop- 
erties, the  compound  having  new  and  different  properties, 
Boyle  distinctly  placed  himself  on  the  plane  of  the  modern 
chemist.  Differences  in  affinity  were  also  recognized  by 
him  in  preparing  tables  giving  the  relative  affinity  of 
various  metals  towards  the  acids.  Several  chemists 
busied  themselves  with  such  lists  in  later  years. 


CHAPTER  V 

THE  CHEMISTRY  OF  COMBUSTION 

The  most  important  reaction  in  chemistry  is  that  of 
oxidation,  known  in  its  common,  everyday  occurrence 
as  combustion.  A  rational  and  satisfactory  explanation 
of  this  process  was  therefore  a  fundamental  necessity 
for  the  progress  of  the  science.  Some  progress  might  be 
attained  under  a  false  theory  but  there  would  be  many 
misconceptions  and  errors.  The  theory  of  combustion 
which  prevailed  through  most  of  the  eighteenth  century 
was  called  the  phlogiston  theory.  This  theory  was 
first  imperfectly  stated  by  Becher  in  the  latter  part  of 
the  seventeenth  century  but  was  more  clearly  given  by 
Stahl,  who  introduced  the  term  phlogiston,  or  fire  sub- 
stance. Both  of  these  were  German  chemists.  Since 
the  theory  was  false,  it  obscured  or  twisted  facts  and 
necessarily  retarded  progress. 

Phlogiston  Theory.  —  The  theory  may  be  briefly  stated 
as  follows.  The  purpose  was  to  explain  the  changes 
which  occur  when  a  metal  is  heated  in  the  air  and  changed 
into  a  powder.  The  metal  was  said  to  be  calcined  and  the 
resulting  powder  was  called  a  calx.  Of  course  the  burn- 
ing of  wood  or  coal  with  the  formation  of  ashes  and  many 
similar  operations  come  under  the  same  heading.  Ac- 
cording to  the  phlogistics,  as  they  were  called,  the  metals 
lost  something  which  was  the  hypothetical  phlogiston  and 
the  calx  remained.  The  metal,  then,  was  a  compound 

34 


THE  CHEMISTRY  OF  COMBUSTION  35 

made  up  of  calx  and  phlogiston.  This  phlogiston  was 
present  in  all  combustible  substances  as  coal,  inflam- 
mable gases,  etc.,  and  some  substances  contained  more 
than  others.  The  supposed  proof  of  the  theory  lay  in 
the  fact  that  when  a  metallic  calx  was  heated  with  a 
substance  rich  in  phlogiston,  such  as  coal,  the  metal 
could  be  restored.  Thus,  when  iron  was  heated  in  the 
ah-  a  red  calx  was  formed,  copper  gave  a  black  calx,  and 
metallic  iron  or  copper  could  be  recovered  by  heating 
these  with  coal. 

The  question  was  asked:  What  is  this  phlogiston  and 
why  can  no  one  get  hold  of  it  to  examine  it?  Wild  and 
absurd  conjectures  were  made  as  to  its  nature,  some  of 
these  placing  it  beyond  experimental  evidence.  Again 
the  question  of  weight  relations  arose,  thus  appealing  to 
the  balance,  and  it  was  found  that  the  calx  weighed  more 
than  the  original  metal.  How  could  that  be  possible 
if  the  metal  had  lost  something?  The  explanation  offered 
as  to  this  was  that  when  wood  was  burned  the  flame 
ascended  and  hence  the  fire  substance,  or  phlogiston, 
possessed  levity  rather  than  gravity  and  when  combined 
in  substances  made  them  lighter.  The  trouble  was  that 
the  discussion  became  one  of  logic  with  neglect  or  dis- 
regard of  facts.  One  of  the  last  of  the  phlogistics  was 
Priestley,  who  argued  stubbornly  in  behalf  of  his  views 
until  his  .death  in  1804. 

Composition  of  Air.  —  One  of  the  causes  of  the  failure 
to  recognize  the  true  explanation  of  combustion  was 
ignorance  as  to  the  composition  of  the  air  which  was 
essential  to  all  combustions.  Of  course  the  necessity  for 
ah*  in  burning  anything  had  been  recognized  in  very  early 
times.  The  phlogistics  explained  this  by  maintaining 


36  HISTORY  OF  CHEMISTRY 

that  phlogiston  could  not  escape  unless  combined  with 
air.  Animals  breathing  in  air  were  supposed  to  breathe 
out  phlogiston. 

Hooke's  Theory  of  Combustion.  —  During  the  latter 
half  of  the  eighteenth  century  there  were  three  dis- 
tinguished chemists  in  England,  all  of  them  adherents  of 
the  phlogiston  theory  and  its  earnest  defenders.  These 
were  Black,  Cavendish,  and  Priestley.  They  were  either 
in  ignorance  of  or  attached  no  importance  to  the  theory 
of  Hooke,  their  fellow  countryman,  as  to  combustion. 
This  theory,  published  in  1665  in  his  Micographia, 
claimed  to  be  based  upon  experiment.  It  is  contained 
in  twelve  propositions  but  may  be  briefly  stated  as  follows : 
Air  supports  combustion  but  this  combustion  will  take 
place  only  after  the  substance  has  been  sufficiently  heated. 
There  is  no  such  thing  as  elemental  fire.  This  combustion 
is  caused  by  a  substance  inherent  in  and  mixed  with  the 
air  which  is  very  much  like,  if  not  the  very  same  as  that 
which  is  fixed  in  saltpeter.  Mayow  a  little  later  recog- 
nized that  the  air  contains  a  substance  which  unites 
with  metals  when  they  are  calcined.  This  substance  will 
also  change  venous  blood  to  arterial,  as  shown  by  the 
color.  It  is  contained  in  saltpeter,  for  substances  burn 
when  mixed  with  saltpeter.  He  therefore  called  this 
component  of  the  air  spiritus  nitro-aerius. 

It  was  the  discovery  of  oxygen  that  struck  the  death 
blow  to  the  phlogiston  theory.  Strange  to  say  it  was 
discovered  and  identified  in  J774^by  Priestley  and  inde- 
pendently by  Scheele,  both  of  them  phlogistics,  who 
failed  to  grasp  its  bearing  upon  the  phlogiston  theory. 
In  the  hands  of  Lavoisier,  the  great  Frenchman,  it  revealed 
the  secret  of  combustion.  Priestley  visited  Paris  and 


THE  CHEMISTRY  OF  COMBUSTION  37 

showed  Lavoisier  how  to  prepare  it  by  first  heating  mer- 
cury in  the  air  until  the  red  precipitate  was  formed. 
When  this  was  placed  under  a  bell-jar  from  which  the 
air  had  been  pumped  and  was  heated,  the  original  mercury 
was  regained  with  liberation  of  a  gas  which  would  support 
combustion.  By  weighing  the  mercury,  then  the  red 
precipitate  and  the  gas  given  off,  it  was  shown  by  Lavoisier 
that  the  increase  in  weight  of  the  mercury  in  forming 
the  red  precipitate  or  calx  corresponded  with  the  weight 
of  gas  which  was  taken  up  by  it.  Lavoisier  called  this 
gas  oxygen  or  the  acid-producer.  Priestley  called  it  de- 
phlogisticated  air.  The  discovery  of  hydrogen  by  Cav- 
endish and  the  fact  that  on  burning  it  formed  water 
completed  the  proof  of  the  new  theory  that  combustion  is 
simply  combining  with  oxygen  or  oxidation.  Cavendish 
called  this  gas  inflammable  air  but  Lavoisier  named  it 
hydrogen  or  the  water-former. 


CHAPTER  VI 

THE  NEW  CHEMISTRY 

It  is  manifest  from  the  preceding  pages  that  chemistry 
was  now  developing  into  a  science.  The  gathering  of 
facts  was  going  on  apace.  The  chief  lack  was  a  rational 
system  of  arrangement  based  on  the  distinctive  charac- 
teristics of  the  substances  involved.  A  distinction  had 
already  been  drawn  between  compounds  and  elements. 
An  element  was  a  simple  body  made  up  of  just  one  kind 
of  matter.  For  instance,  no  lighter  nor  heavier  substance 
could  be  got  from  it.  A  compound  was  made  up  of  two 
or  more  different  substances.  Since  the  term  element 
was  still  in  great  measure  reserved  for  the  four  primal 
principles  of  the  Greeks,  what  we  now  call  elements  were 
spoken  of  as  simple  bodies.  The  finding  of  new  elements 
and  compounds  now  depended  upon  analytical  results. 

Analysis.  —  Tests  for  the  elements  had  to  be  devised 
depending  upon  their  specific  properties.  To  simplify 
the  work  these  tests  must  be  systematically  arranged. 
Analysis  in  the  wet  way  was  first  outlined  by  Boyle  and 
chiefly  applied  to  mineral  waters,  which  attracted  much 
interest  and  investigation.  Bergman  (1735-1784),  a 
Swedish  chemist  and  professor  at  the  University  of 
Upsala,  enlarged  the  number  of  reagents  and  studied 
their  action  on  such  substances  as  occur  most  commonly. 
This  branch  of  the  science  then  began  to  be  exact .  In  quan- 
titative analysis,  also,  he  took  an  important  step  forward 

38 


THE  NEW  CHEMISTRY  39 

in  abandoning  the  plan  of  actually  isolating  the  various 
constituents  and  introduced  the  method  of  transform- 
ing each  constituent  into  some  compound  whose  exact 
composition  was  known  and  which  could  be  easily  iso- 
lated. Sometimes  the  composition  was  unknown  and  the 
simple  body  present  had  never  been  separated,  as  silica 
or  alumina,  and  in  such  cases  the  analyst  had  to  content 
himself  with  separating  the  compound  which  was  to  him, 
for  all  intents  and  purposes,  a  simple  body.  Bergman 
analyzed  a  large  number  of  minerals  and  other  substances. 
For  those  which  he  could  not  dissolve  in  water  or  acids 
he  introduced  the  method  of  fusion  with  caustic  or  car- 
bonated alkalies  so  as  to  bring  them  into  solution,  a  most 
important  addition  to  analytical  methods.  Some  of  his 
researches  were  masterly  and  quite  in  the  spirit  of  the 
present  time.  Such,  for  example,  was  his  work  on  the 
differences  between  wrought  iron,  steel,  and  cast  iron; 
also  upon  the  cause  of  "cold  shortage"  in  iron.  Sweden 
produced  much  iron  and  this  made  the  work  of  Bergman 
especially  important  for  his  native  land.  He  also  analyzed 
the  air  and  reported:  " Common  air  is  a  mixture  of  three 
elastic  fluids;  free  aerial  acid  (carbonic  acid)  but  in  such 
small  quantities  that  it  does  not  sensibly  alter  the  color  of 
litmus;  an  air  which  can  neither  serve  for  combustion  nor 
for  the  respiration  of  animals,  which,  therefore,  we  call 
vitiated  air  until  we  know  its  nature  perfectly;  and  lastly 
an  air  absolutely  necessary  for  fire  and  for  animal  life 
which  forms  pretty  nearly  the  fourth  part  of  common  air 
and  which  I  regard  as  pure  air."  In  this  he  was  the  first  to 
give  a  clear  statement  as  to  the  quantitative  composition 
of  air.  This  was  based  on  his  own  and  on  Scheele's 
experiments. 


40  HISTORY  OF  CHEMISTRY 

Scheele  (1742-1786).  —  Probably  no  one  before  nor 
since  his  day  has  made  so  many  important  discoveries 
as  Scheele,  a  fellow  countryman  of  Bergman.  He  was 
a  pharmacist,  poor  and  reserved,  and  yet  out  of  his 
poverty  and  imperfect  appliances  achieved  wonderful 
success  in  mastering  nature's  secrets  in  his  short  life 
of  forty-three  years.  His  letters  have  been  published  in 
modern  times  and  they  reveal  how  much  he  knew  and  how 
far  he  was  ahead  of  his  contemporaries.  His  first  work 
was  upon  the  organic  acids,  many  of  which  he  isolated 
and  examined.  Among  organic  acids  he  discovered  tar- 
taric,  oxalic,  malic,  citric,  and  gallic;  among  inorganic, 
molybdic,  tungstic,  and  arsenic.  Three  elements  were 
discovered  by  him,  oxygen,  manganese,  and  chlorine; 
and  one  new  alkaline  earth,  baryta.  He  prepared  oxygen 
by  heating  manganese  dioxide  in  the  same  year  that 
Priestley  prepared  it  from  mercuric  oxide.  His  chief  de- 
ficiency lay  in  the  matter  of  understanding  phenomena 
and  formulating  theories.  It  is  evident  that  his  acceptance 
of  the  phlogiston  theory  led  him  astray  in  this. 

Analysis  of  Air.  —  Scheele  examined  the  atmosphere 
with  a  view  to  determining  what  part  it  played  in  the 
phenomena  of  combustion.  First,  he  tried  the  action  of 
various  substances  upon  the  air.  These  substances  were 
supposed  to  contain  phlogiston  and  hence,  he  reasoned, 
would  give  it  off  to  the  air  held  in  a  closed  space.  Some 
of  the  substances  experimented  upon  were  moist  iron 
filings,  fresh  moist  iron  hydroxide,  etc.  He  observed  that 
the  air  diminished  in  amount  and  that  the  portion  left 
was  incapable  of  supporting  combustion.  This  diminu- 
tion of  volume  he  thought  was  due  to  an  absorption  of 
phlogiston  by  the  air,  and  hence  the  air  should  be  specifi- 


THE  NEW  CHEMISTRY  41 

cally  heavier.  To  his  surprise  he  found  the  opposite  to 
be  true.  A  part  of  the  air  had  disappeared  and  the 
remainder  was  specifically  lighter.  Scheele  concluded 
that  the  atmosphere  consisted  of  two  different  kinds  of 
air  —  one  having  no  power  of  taking  up  phlogiston  and 
hence  being  left  behind  in  combustions,  the  other  taking 
up  phlogiston  in  an  enhanced  degree.  This  was  his  fire- 
air,  or  Lavoisier's  oxygen,  though  as  yet  unknown  to  the 
great  French  chemist.  His  experiments  as  to  the  relative 
proportions  of  these  two  constituents  fall  far  behind  in 
accuracy  those  made  a  little  later  by  Cavendish.  He 
pursued  his  investigation  further  and  was  badly  misled 
by  the  phlogiston  fancy.  Thus,  in  explanation  of  the 
experiment  just  described,  he  concluded  that  the  union 
of  phlogiston  with  one  part  of  the  air  caused  a  diminution 
in  volume  because  a  tenuous,  delicate  substance  had  been 
formed  and  this  escaped  through  the  pores  of  the  glass 
vessel.  This  delicate  substance  was,  in  his  opinion, 
fire  or  heat.  Fire  then  was  a  compound  of  fire-air  and 
phlogiston.  This  fire  or  heat  he  believed  could  be  de- 
composed into  its  constituents  by  the  use  of  such  sub- 
stances as  would  combine  with  the  phlogiston  and  set 
the  fire-air  free.  He  thought  he  could  do  this  with  nitric 
acid.  He  distilled  niter  and  oil  of  vitriol,  or  sulphuric 
acid,  and  obtained  nitric  acid  and  a  gas  which  supported 
combustion  better  than  the  air  itself.  This  supposed 
decomposition  of  heat  he  effected  further  by  heating  other 
substances  as  manganese  dioxide  and  niter.  Thus  he 
isolated  oxygen  or  fire-air,  as  he  called  it. 

Boerhaave  (1668-1738). —  There  was  in  Holland  at 
this  time  a  very  influential  chemist  named  Boerhaave, 
who  was  a  professor  at  the  University  of  Leyden  and  who 


42  HISTORY  OF  CHEMISTRY 

did  much  to  clear  the  way  for  the  new  chemistry  by  ex- 
posing the  errors  of  the  alchemists  and  their  successors 
and  the  falsity  of  their  views.  He  tested  with  care  and 
accuracy  everything  that  he  taught,  and  spared  neither 
pains  nor  time  to  have  his  observations  correct.  For 
instance,  the  alchemists  maintained  that  mercury  could 
be  fixed  in  the  form  of  a  fireproof  metal  without  the 
addition  of  any  other  substance.  Boerhaave  kept  mercury 
at  a  somewhat  raised  temperature  in  an  open  vessel  for 
fifteen  years  without  noting  any  change.  So,  too,  when 
heated  higher  in  a  closed  vessel  for  six  months  no  change 
could  be  detected.  It  had  also  been  maintained  that  if 
mercury  were  repeatedly  distilled,  a  more  volatile  essence 
with  peculiar  properties  could  be  obtained.  Boerhaave 
carried  out  this  distillation  five  hundred  times  without 
securing  the  essence.  His  skill  in  interpreting  facts  and 
the  clearness  of  his  theoretical  views  made  him  an  excellent 
teacher,  and  his  text-book  on  chemistry  went  through  re- 
peated editions  and  translations  into  other  languages  and 
was  used  for  many  years  after  his  death.  He  seemed  to 
take  little  notice  of  the  phlogiston  theory. 

Fixity  of  proportions.  —  It  is  noteworthy  that  another 
foundation  stone  was  being  laid  without  discussion  or 
statement,  and  that  was  in  the  general  acceptance  of 
the  essential  conception  that  the  constituents  of  each 
definite  compound  were  always  in  the  same  definite  pro- 
portion. This  grew  naturally  out  of  the  experience  of 
the  analytical  chemist  who  tested  the  quantitative  re- 
lations with  his  balance.  If  these  proportions  were 
not  fixed  his  analytical  work  was  futile.  No  question 
was  raised  concerning  this  until  the  close  of  the  century. 

Berthollet    (1748-1822).  — About    the    beginning    of 


THE  NEW  CHEMISTRY  43 

the  nineteenth  century  the  question  was  taken  up  by 
Berthollet,  one  of  the  first  and  ablest  of  Lavoisier's  sup- 
porters. He  contended  that  these  proportions  were 
not  constant  but  that  the  relative  masses  of  the  combin- 
ing substances  determined  the  proportions  in  which 
they  would  unite  to  form  compounds.  His  views  met 
with  immediate  opposition  on  the  part  of  leading  chem- 
ists and  gave  a  new  direction  to  their  investigations. 
His  chief  antagonist  was  his  fellow  countryman,  Proust, 
and  the  exact  quantitative  composition  of  many  com- 
pounds was  worked  out.  In  the  course  of  these  investi- 
gations it  was  found  that  metals  might  have  several 
oxides  and  also  that  hydroxides  existed.  The  victory 
finally  remained  with  Proust.  This  problem  has  arisen 
in  subsequent  years  as  analytical  methods  improved 
greatly  in  exactness,  but  the  definiteness  of  proportions 
seems  established. 

Views  as  to  Affinity.  —  Several  chemists  had  turned 
their  attention  to  the  attractive  force  which  brought 
about  combination  between  different  substances  and 
held  together  the  different  particles  in  a  compound. 
The  name  affinity  had  been  given  early  to  this  combin- 
ing force.  While  there  was  no  measure  for  this  force  nor 
theorizing  as  to  its  nature,  several  chemists  endeavored 
to  settle  the  relative  strength  of  attraction  between 
different  substances  and  constructed  what  were  called 
affinity  tables.  The  question  comes  down  to  this :  Which 
metal,  iron  or  copper  or  lead,  has  the  greatest  affinity 
for  sulphur;  or  which  acid  has  the  greatest  affinity  for 
soda?  Such  tables  were  helpful  in  those  times  but  failure 
to  recognize  the  influence  of  other  factors  made  them  of 
slight  scientific  value.  Bergman's  table  was  one  of  the 


44  HISTORY  OF  CHEMISTRY 

best  of  these  early  efforts,  since  it  shows  a  knowledge 
that  affinity  phenomena  depend  upon  the  temperature 
and  physical  state. 

RELATIVE  AFFINITY  FOR  SULPHURIC  ACID 

Wet  Way  Dry  Way 

Baryta  Phlogiston 

Potash  and  soda  Baryta 

Ammonia  Potash 

Alumina  Soda 

Zinc  oxide  Lime 

Iron  oxide  Magnesia 

Copper  oxide  Metallic  oxides 

Mercury  oxide  Ammonia 

Silver  oxide  Alumina 

Berthollet  has  exerted  a  lasting  influence  upon  the 
views  concerning  affinity  and  showed  in  high  degree 
the  power  of  abstract  conception  and  logical  develop- 
ment of  chemical  ideas.  He  reasoned  that  affinity  was 
by  no  means  a  simple  force  and  easy  to  determine  and 
measure,  but  was  influenced  by  temperature,  physical 
state,  cohesion,  and  especially  by  mass.  The  latter  largely 
determined  the  course  of  chemical  reactions.  Thus  rock 
made  up  of  the  hardest  silicates  is  weathered  or  grad- 
ually decomposed  by  the  action  of  rain  containing  one 
of  the  weakest  of  acids,  carbonic  acid. 

Lavoisier  (1743-1794).  —  The  materials  were  now 
gathered  and  the  architect  and  builder  was  at  hand. 
Lavoisier  has  justly  been  called  the  Father  of  Modern 
Chemistry.  Born  in  Paris,  carefully  educated,  gifted 
in  intellect,  accurate  in  work,  and  with  a  clear,  far-seeing 
vision,  he  was  one  of  that  type  which  is  born  now  and 
then  in  time  of  need  to  point  out  the  path  for  succeed- 


THE  NEW  CHEMISTRY  45 

ing  generations.  There  may  be  many  priests  in  the 
temple  of  science  but  only  at  long  intervals  does  a  pro- 
phet arise.  At  the  early  age  of  twenty-one  he  was  awarded 
a  medal  by  the  government  for  a  memoir  upon  the  best 
and  most  economical  method  of  lighting  the  streets 
of  a  city,  and  at  twenty-five  he  was  chosen  an  adjunct 
member  of  the  French  Academy.  Chemistry  did  not 
receive  the  whole  of  his  attention  at  first  but  shared  it 
with  geology,  mineralogy,  and  mathematics.  The  re- 
markable discoveries  which  were  being  made  in  chemistry, 
especially  in  connection  with  gases  and  the  atmosphere, 
drew  him,  however,  to  devote  all  his  energies  to  chem- 
istry. For  more  than  twenty  years  he  was  indefatigable 
as  a  worker,  repeating  the  experiments  of  others  and 
pursuing  fresh  lines  of  inquiry.  And  then  his  life  and 
activities  were  cut  short  by  the  coming  on  of  the  French 
Revolution.  He  was  executed  by  Robespierre  in  1794 
at  the  age  of  fifty-one. 

Character  of  his  work.  —  Lavoisier's  most  valuable 
services  were  as  an  interpreter  of  his  own  work  and  that 
of  others.  He  showed  a  clear  insight  into  the  causes  of 
phenomena,  a  quick  perception  of  the  importance  of  the 
many  discoveries  of  his  time,  and  a  comprehensive  grasp 
of  facts  and  their  inter-relation  and  connection.  These 
powers  enabled  him  to  detect  the  errors  and  falsity 
in  the  theory  and  reasoning  of  the  chemists  of  his  age 
and  to  lay  the  basis  for  the  new  chemistry  of  the  quan- 
titative era.  Exclusive  importance  had  been  attached 
hitherto  to  visible  phenomena,  whereas  he  introduced 
a  deeper  study  of  chemical  reactions  and  the  relations 
of  quantity. 

Experiments  on  Combustion.  —  In  1774  he  published 


46  HISTORY  OF  CHEMISTRY 

his  first  strictly  scientific  volume  under  the  title:  Essays 
Physical  and  Chemical.  In  this  he  described  all  that 
had  been  done  on  the  subject  of  gases  from  the  time 
of  Paracelsus  down  through  the  work  of  Priestley.  He 
also  gave  an  account  of  his  own  experiments.  He  showed 
that  when  metals  were  calcined  their  weights  increased 
and  that  a  portion  of  air,  equal  to  their  increase  in  weight, 
had  been  absorbed  from  the  surrounding  atmosphere. 
He  burned  phosphorus  in  the  air  and  observed  the 
decrease  in  the  volume  of  the  air  and  the  increase 
in  the  weight  of  the  phosphorus.  We  are  apt  to  think 
that  the  mere  proof  that  the  metallic  calx  weighed  more 
than  the  metal  was  sufficient  to  disprove  the  phlogiston 
theory.  Both  parts  of  the  proof  given  by  Lavoisier  were 
necessary  and  even  then  he  felt  it  to  be  insufficient  and 
merely  preliminary  to  his  final  work.  It  had  already 
been  shown  that  the  calces  were  heavier  than  the  metals 
from  which  they  came  and  that  they  were  specifically 
lighter,  but  the  phlogistic  chemists  had  disregarded 
these  weight  relations,  taking  refuge  in  the  hypothesis 
of  a  phlogiston  unaffected  by  gravity  or  actually  making 
substances  lighter  by  its  presence. 

Composition  of  the  Atmosphere.  —  In  Lavoisier's 
further  attack  upon  the  phlogiston  theory  he  examined 
the  atmosphere  and  its  constituents.  In  the  book  men- 
tioned above  he  tells  nothing  to  indicate  that  he  knew 
the  composition  of  the  air  or  the  distinct  nature  of  oxy- 
gen. These  were  discoveries  reserved  for  Scheele  and 
Priestley,  but  Lavoisier  was  evidently  very  near  to 
their  discovery  and  was  only  anticipated  in  this.  When 
Priestley  visited  him  shortly  afterwards  and  showed 
him  how  to  prepare  oxygen  from  the  red  oxide  of  mer- 


THE  NEW  CHEMISTRY  47 

eury,  Lavoisier  immediately  saw  what  the  discovery- 
meant  and  how  it  made  plain  much  that  was  unexplained 
in  his  own  work.  It  altered  his  views  and  suggested  to 
him  the  nature  of  atmospheric  air  and  of  the  changes 
taking  place  in  the  calcination  of  the  metals.  For  twelve 
years  he  worked  over  these  problems,  performing  a  great 
number  of  experiments  with  an  accuracy  hitherto  un- 
known. He  then  boldly  proclaimed  the  non-existence 
of  phlogiston  and  replaced  this  old  theory  by  a  new  one, 
explaining  the  phenomena  of  combustion  and  reduc- 
tion as  due  to  the  combination  with  oxygen  or  its  separa- 
tion. He  first  won  to  his  views  the  distinguished  French 
chemists  of  his  day,  and  before  many  years  all  men  of 
standing  in  the  science  gave  in  their  adherence  to  the 
new  explanation  offered  by  him,  except  a  few  who  could 
not  give  up  views  which  had  formed  the  basis  of  all 
their  scientific  work.  The  year  1786  may  be  fixed  as  the 
date  of  the  overturning  of  the  old  theory. 


CHAPTER  VII 

THE  FOUNDATIONS 

Composition  of  Water.  —  Lavoisier's  triumph  over 
the  supporters  of  the  phlogiston  theory  was  complete 
when  he  made  public  his  researches  upon  the  composi- 
tion of  water.  The  hydrogen  evolved  when  a  metal 
was  acted  upon  by  an  acid  was  considered  at  first  by  some 
to  be  identical  with  the  hypothetical  phlogiston  and 
Cavendish,  the  discoverer  of  hydrogen,  maintained  this 
view  to  the  end  of  his  life.  When  Cavendish's  further 
discovery  of  the  formation  of  water  by  the  burning 
of  hydrogen  was  told  to  him  Lavoisier  saw  his  way  to 
solution  of  this  puzzle  and  lost  no  time  in  repeating  so 
important  an  experiment.  The  explanation  he  offered 
to  the  reaction  between  the  acid  and  the  metal  was 
that  the  hydrogen  came  from  the  water,  which  took  part 
in  the  reaction;  at  the  same  time  the  oxygen  combined 
with  the  metal  and  thus  it  was"*  not  the  metal  but  the 
metallic  oxide  which  was  dissolved  by  the  acid.  In  other 
cases,  as  in  the  action  of  nitfic  acid  upon  copper,  the 
metal  decomposed  the  acid  and  not  the  water,  taking 
oxygen  from  it  to  form  an  oxide,  and  this  was  dis- 
solved by  the  remainder  of  the  acid.  The  deoxidized  part 
of  the  acid,  he  said,  escaped  as  a  gas.  A  prophet  in  chem- 
istry is  not  inspired  and  can  only  do  his  best  with  such 
facts  as  are  known  to  him.  Hence  one  must  be  lenient  as 
to  the  instances  in  which  these  views  (ail  of  the  full  truth. 

48 


THE  FOUNDATIONS  49 

Transmutation  of  Water.  —  One  of  Lavoisier's  early 
investigations  bore  upon  the  nature  of  water  and  well 
illustrates  his  accuracy,  thoroughness,  and  acute  reason- 
ing. It  had  been  noted  by  many  earlier  investigators 
that  when  pure  water  was  boiled  for  a  long  time  in  a 
glass  vessel  a  white  residue  was  found  in  the  vessel  after 
evaporation.  This  was  long  regarded  as  a  conclusive 
proof  that  water  could  be  changed  into  earth.  Appeal- 
ing to  the  balance  as  arbiter,  he  first  weighed  his  glass 
vessel  and  then,  after  heating  pure  water  in  it  for  one 
hundred  days,  found  there  was  no  change  in  the  weight 
of  the  vessel  and  its  contents;  that  is,  the  vessel  and 
the  water  weighed  the  same  after  the  heating  as  before. 
When  the  water  was  removed  the  vessel  weighed  less  than 
the  original  weight  of  the  empty  vessel.  When  he  evap- 
orated the  water  he  obtained  a  residue  which  he  found 
corresponded  in  weight  to  the  loss  in  weight  of  the  empty 
vessel.  He,  therefore,  concluded  that  water  on  being 
heated  is  not  changed  into  earth  but  that  a  part  of  the 
matter  of  which  the  glass  is  composed  is  dissolved  by  the 
water.  The  analytical  work  of  Scheele  afterwards  showed 
that  this  residue  had  the  same  components  as  the  glass, 
thus  confirming  the  work  of  Lavoisier.  The  old  notion 
of  transmutation  was  thus  proved  to  be  false  and  the 
important  generalization  was  established  that  matter 
can  neither  be  destroyed  nor  created.  This  principle 
of  the  conservation  of  mass  is  one  of  the  fundamental 
laws  of  science.  Of  course,  Lavoisier's  work  was  only 
the  beginning  of  the  series  of  experiments  on  this  sub- 
ject which  after  many  years  established  the  law. 

The  Atmosphere.  —  Priestley  performed  various  ex- 
periments upon  the  gases  known  to  him  with  the  aid 


50  HISTORY  OF  CHEMISTRY 

of  the  pneumatic  trough  which  he  practically  invented. 
He  discovered  the  relation  of  plants  and  animals  to  the 
atmosphere  and  the  approximate  balance  maintained 
by  their  action  upon  it.  His  inaccurate  analytical  work 
and  his  devotion  to  the  phlogiston  theory  prevented 
his  reaching  a  true  explanation  of  the  facts  observed 
by  him.  Scheele  determined  the  composition  of  the  at- 
mosphere, and  later  Cavendish  made  an  exact  analysis 
of  it.  Lavoisier  had  shown  that  it  consisted  of  oxygen 
and  nitrogen  and  had  determined  the  proportions  of 
each.  He  was,  therefore,  in  a  position  to  complete  and 
explain  the  work  of  Priestley.  The  processes  of  breathing 
and  of  calcination  were  chemically  analogous.  Oxygen 
was  drawn  into  the  lungs  by  the  respiration  of  animals, 
and  there  he  thought  it  combined  with  carbon  and  the 
carbonic  acid,  or  the  "fixed  air"  of  Black,  was  breathed 
out.  This  was  noxious  to  other  animals  and  this  it  was 
which  was  removed  by  plants. 

The  Nature  of  Heat  and  of  Matter.  —  Lavoisier  dis- 
proved the  old  ideas  as  to  the  elemental  nature  of  heat; 
yet  apparently  he  believed  it  to  have  material  existence. 
He  wrote  of  a  matiere  de  chaleur  which  he  also  called 
calorique.  He  ascribed  to  it  a  fluid  (gaseous)  nature 
but  said  it  had  no  weight.  His  idea  and  also  his  views 
upon  the  constitution  of  matter  are  perhaps  best  given 
by  a  citation  from  his  Reflexions  sur  le  Phlogistique. 
Matter,  he  says,  consists  of  small  particles  which  do  not 
touch  one  another,  otherwise  the  diminution  in  volume 
on  cooling  could  not  be  explained;  between  these  par- 
ticles is  the  calorique.  In  gases  there  is  most  of  this  calo- 
rique; in  solids  least.  In  his  experiments  with  Laplace 
upon  specific  heat  he  showed  that  solids  differ  in  their 


THE  FOUNDATIONS  51 

capacity  for  taking  up  this  heat.  His  views  are  in  par- 
tial accord  with  the  modern  theory  of  heat  when  he  comes 
to  define  that  form  of  energy.  He  says,  "Heat  is  the 
result  of  invisible  motion  of  the  particles,  the  sum  of 
the  product  of  the  masses  multiplied  by  the  square  of 
the  velocities." 

Investigation  of  Organic  Substances.  —  Lavoisier 
also  occupied  himself  with  organic  chemistry,  or  the 
chemistry  of  life  products,  and  made  a  beginning  towards 
a  scientific  study  of  it  in  devising  a  method  of  analysis 
by  which  these  substances  could  be  burned  and  the  water 
and  carbon  dioxide  formed  could  be  measured.  Of 
course  such  a  method  was  impossible  until  the  compo- 
sition of  these  two  substances  themselves  was  definitely 
fixed.  That  these  substances,  as  well  as  carbon  in  imper- 
fect combustions,  were  formed  on  burning  organic  sub- 
stances had  long  been  known.  Their  nature,  however, 
and  the  question  as  to  their  pre-existence  in  the  or- 
ganic substances  had  been  the  subject  of  much  discussion. 
Through  his  analysis  Lavoisier  determined  that  all 
organic  substances  were  composed  of  carbon  and  hydro- 
gen, sometimes  oxygen,  and  less  often  nitrogen  and 
other  elements. 

Theory  as  to  Acids.  —  Thus  much  false  theory  and 
confusion  in  the  science  had  been  removed  and  the  founda- 
tions for  a  new  system  had  been  laid.  Simple  bodies  or 
elements  were  recognized;  these  formed  compounds  by 
the  union  of  their  particles  drawn  together  by  an  attrac- 
tive force,  affinity,  and  heat  had  its  part  to  play  in  these 
masses.  The  multiplicity  of  compounds  made  necessary 
a  system  in  their  arrangement  —  such  a  system  as  would 
bring  out  and  explain  their  interrelations.  The  funda- 


52  HISTORY  OF  CHEMISTRY 

mental  reaction  was  oxidation.  Lavoisier  recognized 
the  parts  played  by  oxygen  in  the  formation  of  acids, 
of  oxides,  and  of  salts.  For  these  he  gave  the  simple 
definitions  which  form  the  foundations  of  the  new  chem- 
istry. 

1.  An  acid  results  from  the  union  of  a  simple  body, 
ordinarily  non-metallic,   with  oxygen. 

2.  An  oxide  is  a  compound  of  a  metal  and  oxygen. 

3.  A  salt  is  a  compound  of  a  metal  and  oxygen. 
This  system  was  extended  further  for  the  sulphides, 

phosphides,  etc.,  but  the  true  nature  of  the  chlorides  was 
not  known  and  the  hydracids  were  discovered  some  years 
later.  With  their  discovery  the  part  played  by  hydrogen 
became  clearer,  but  a  century  had  to  pass  before  this 
could  be  even  approximately  explained. 

The  overthrow  of  the  followers  of  Stahl  and  the  accept- 
ance of  Lavoisier's  ideas  ushered  in  a  new  era  in  chem- 
istry. A  new  nomenclature  was  called  for  and  it  was 
created  by  Lavoisier  and  the  French  Encyclopedists. 
Of  course,  as  knowledge  grew  mistakes  had  to  be  cor- 
rected and  changes  made,  but  the  essential  foundations 
had  been  laid. 

Elements.  —  It  will  be  helpful  here  to  trace  the  growth 
in  the  ideas  regarding  the  elements,  as  the  proper  defi- 
nition of  these  was  one  of  the  most  important  and  far- 
reaching  changes  introduced  by  the  new  system.  Al- 
chemists and  chemists  seemingly  had  not  attached 
much  importance  to  this  matter  up  to  this  time  and  the 
distinctions  drawn  were  rather  hazy.  Hitherto  the 
name  had  covered  mainly  philosophical  speculations; 
henceforward  they  were  to  form  the  basis  of  systematic 
chemistry.  The  four-element  theory  of  Empedokles 


THE  FOUNDATIONS  53 

and  Aristotle  was  a  dream,  a  philosophical  figment  with- 
out basis  or  confirmation  in  real  experiments.  These 
elements  were  regarded  as  principles  with  certain  mate- 
rial characteristics,  entering,  all  or  some  of  them,  into 
every  known  substance  and  not  necessarily  capable  of 
independent  existence  themselves.  Some  chemists,  in- 
deed, undertook  to  prove  that  certain  substances  did 
contain  these  principles.  There  was  no  attempt,  how- 
ever, at  a  general  proof. 

The  first  clarifying  definition  was  given  by  Boyle 
(1661),  who  was  far  ahead  of  his  times.  He  defined  ele- 
ments as  ''certain  primitive  and  simple  bodies  which, 
not  being  made  up  of  any  other  bodies,  or  of  one  another, 
are  the  ingredients  of  which  all  those  called  perfectly 
mixed  bodies  are  immediately  compounded,  and  into 
which  they  are  ultimately  resolved."  He  did  not  be- 
lieve himself  warranted  by  the  knowledge  then  pos- 
sessed in  proclaiming  the  positive  existence  of  such 
elements. 

During  the  phlogistic  period  less  and  less  importance 
was  attached  to  the  old  ideas  as  to  elements,  and  the 
belief  gradually  sprang  up  that  a  true  element  must  be 
something  which  could  be  prepared  and  was  not  sub- 
ject to  change.  Macquer,  in  his  Dictionary  of  Chem- 
istry, defined  elements  as  "those  bodies  which  are  so 
simple  that  they  can  not  by  any  known  method  be  decom- 
posed or  even  altered  and  which  also  enter  as  princi- 
pal or  constituent  parts  into  the  composition  of  other 
bodies  which  are  therefore  called  compound  bodies." 
But  he  adds,  "The  bodies  in  which  this  simplicity  has 
been  observed  are  fire,  air,  water,  and  the  purest  earths. " 
Black  proved  that  certain  chemical  substances  were 


54  HISTORY  OF  CHEMISTRY 

possessed  of  a  constant  and  definite  composition  and 
fixed  properties,  unalterable,  and  hence  simple  bodies 
or  elements.  Lastly,  Lavoisier  in  this  Traite  de  Chimie 
enunciated  his  definition  of  an  element  as  follows:  "An 
element  is  a  substance  from  which  no  simpler  body  has 
as  yet  been  obtained;  a  body  in  which  no  change  causes 
a  diminution  of  weight."  Nearer  to  the  modern  theory 
he  could  not  come  without  knowledge  of*  the  atoms  and 
of  allotropism.  Under  such  conditions  a  number  of 
substances  were  classed  as  elements  which  did  not  belong 
to  the  list.  Lavoisier  first  classed  the  metals  as  elements. 
Spread  of  the  New  Chemistry.  —  The  teachings  of 
Lavoisier  or,  as  Fourcroy  styled  it,  the  "French  Chem- 
istry," speedily  found  acceptance  in  France,  in  England, 
and  (through  the  influence  of  Klaproth)  in  Germany, 
where  at  first  the  opposition  had  been  intense.  By  the 
close  of  the  century  chemists  almost  universally  had 
given  in  their  adherence  to  the  new  doctrines.  Chem- 
istry now  had  the  basis  of  a  true  theory  and,  what  was 
of  greater  value,  the  knowledge  that  theories  could  be 
deduced  only  from  the  weight  relations  of  actually  occur- 
ring reactions.  There  were  to  be  no  baseless  and  delu- 
sive dreams  for  the  future,  although  mistakes  might 
be  made  in  the  interpretation  of  facts.  We  find  that 
though  facts  rapidly  increased  in  number  theories  were 
slowly  evolved  and  gained  acceptance  only  after  most 
careful  weighing  and  testing  in  every  known  way.  In 
this  respect  the  experience  of  the  past  was  invaluable. 
Great  names,  so-called  authorities,  might  gain  a  hear- 
ing for  a  theory  but  had  to  show  that  it  was  the  best 
logical  explanation  of  facts  and  laws.  Men  had  cast 
off  forever  the  burden  of  authority  in  science. 


THE  FOUNDATIONS  55 

Black  (1728-1799).  — There  should  be  mentioned 
at  this  time  three  distinguished  chemists,  who  were 
of  great  service  in  making  important  discoveries  and 
improving  methods  and  made  noteworthy  contributions 
to  the  progress  of  chemistry.  The  first  of  these,  Joseph 
Black,  was  of  Scotch  parentage  and,  while  a  "student 
at  the  University  of  Glasgow,  undertook  an  investi- 
gation into  the  cause  of  the  causticity  of  magnesia,  lime, 
and  the  alkalis.  Caustic  lime,  or  quick  lime,  was  made, 
for  instance,  by  the  burning  of  limestone.  Its  caustic- 
ity was  supposed  to  be  conferred  upon  it  by  the  heat 
of  the  fire,  and  this  could  be  transferred  by  the  proper 
treatment  of  a  mild  alkali  with  quick  lime  to  the  caustic 
alkali.  Using  magnesia  alba  in  his  experiments,  he  found 
that  there  was  a  loss  of  weight  on  heating  it  and  the 
substance  magnesia  usta  was  formed.  On  treating  mag- 
nesia alba  (magnesium  carbonate)  with  oil  of  vitriol 
there  was  effervescence  from  an  escaping  gas,  and  epsom 
salt  or  magnesium  sulphate  was  formed.  This  was  also 
formed  from  magnesia  usta  (magnesium  oxide)  and  oil  of 
vitriol  but  there  was  no  escaping  gas.  Mild  alkali  effer- 
vesces on  the  addition  of  oil  of  vitriol  but  caustic  alkali 
does  not.  The  reasoning  then  was  plain.  The  pres- 
ence of  the  gas  set  free  from  magnesia  alba  and  not 
from  magnesia  usta  makes  the  difference  between  the 
two,  and  it  is  also  the  gas  present  in  mild  alkali  which 
enables  it  to  change  magnesia  usta  into  magnesia  alba, 
leaving  caustic  alkali.  The  burning  of  magnesia  alba 
or  of  limestone  consists  then  in  the  driving  off  of  this 
gas  which  Black  called  " fixed  air."  This  fixed  air  was 
afterwards  studied  by  Priestley,  who  invented  the  in- 
valuable pneumatic  trough  to  aid  him  in  his  researches. 


56  HISTORY  OF  CHEMISTRY 

Priestley  identified  this  with  the  gas  issuing  from  fer- 
mentations in  breweries.  Thus  carbon  dioxide  became 
known.  Priestley  later  discovered  carbon  monoxide. 
Black  devoted  much  time  to  experiments  upon  heat  and 
made  the  brilliant  discovery  of  latent  heat,  or  the  heat 
concerned  in  changes  of  physical  state. 

Priestley  (1733-1804).  — The  second  of  these  chem- 
ists was  Priestley  who  was  born  near  Leeds  in  England 
and  was  largely  self  trained,  as  he  had  the  advantage 
of  a  high  school  training  only.  On  account  of  politi- 
cal and  religious  persecution  he  left  England,  and  the 
later  years  of  his  life  were  spent  in  America,  near  Phila- 
delphia. Priestley  was  a  brilliant  investigator,  per- 
forming many  most  striking  experiments.  He  was  not 
thorough,  however,  nor  very  accurate,  possessing  little 
analytical  skill,  and  was  lacking  in  the  scientific  acumen 
needed  for  the  proper  interpretation  of  his  results.  It 
was  upon  the  gases  that  his  most  valuable  work  was 
done,  his  pneumatic  trough  enabling  him  not  only  to 
discover  new  gases  but  to  investigate  the  properties 
of  a  number  of  those  already  partially  known. 

Discovery  of  Oxygen.  —  His  method  of  experimen- 
tation is  well  illustrated  by  his  account  of  his  discovery 
of  oxygen.  "Having  procured  a  lens  I  proceeded  with 
great  alacrity  to  examine  by  the  help  of  it  what  kind 
of  air  a  great  variety  of  substances  would  yield,  put- 
ting them  into  vessels  filled  with  quicksilver  and  kept 
inverted  in  a  basin  of  the  same.  After  a  variety  of  other 
experiments  I  endeavored  to  extract  air  from  mercurius 
calcinatus  per  se  (red  oxide  of  mercury)  and  I  presently 
found  that  by  means  of  this  lens  air  was  expelled  from 
it  very  readily.  Having  got  about  three  or  four  times 


THE  FOUNDATIONS  57 

as  much  as  the  bulk  of  my  materials  I  admitted  water 
to  it  and  found  that  it  was  not  imbibed  by  it.  But  what 
surprised  me  more  than  I  can  well  express  was  that  a 
candle  burned  in  this  air  with  a  remarkably  vigorous 
flame.  I  was  utterly  at  a  loss  to  account  for  it."  His 
experiments  showed  him  that  this  air  "had  all  the  prop- 
erties of  common  air,  only  in  much  greater  perfec- 
tion," and  he  called  it  "  dephlogisticated  air,"  regarding 
it  as  very  pure  ordinary  air. 

Study  of  the  Atmosphere.  —  Priestley  seems  to  have 
looked  upon  all  gases  as  easily  changeable  one  into  the 
other,  at  least  in  the  first  part  of  his  work.  He  made 
many  experiments  as  to  the  action  of  the  various  gases 
known  to  him  upon  animals  and  plants.  He  would  place 
a  mouse  in  a  jar  of  the  gas  and  notice  the  effect  upon  its 
breathing  and  general  life  processes.  Plants  were  grown 
in  similar  jars  and  the  result  upon  the  growth  noted. 
He  showed  that  air,  which  had  become  noxious  through 
breathing  or  the  burning  of  a  candle,  could  be  restored  to 
its  original  condition  by  growing  a  plant  in  it.  This,  he 
said,  was  due  to  the  impregnation  with  phlogiston  in  the 
first  case  and  to  its  removal  in  the  second.  "It  is  very 
probable,"  he  wrote,  "that  the  injury  which  is  continu- 
ally done  to  the  atmosphere  by  the  respiration  of  such 
a  number  of  animals  as  breathe  it  and  the  putrefaction 
of  such  vast  masses  both  of  vegetable  and  animal  sub- 
stances exposed  to  it  is,  in  part  at  least,  repaired  by 
the  vegetable  creation."  He  was  unable  to  explain 
how  this  was  done  as  he  was  a  poor  analyst.  This  lack 
of  analytical  skill  is  shown  in  his  experiments  on  the 
formation  of  water  by  exploding  mixtures  of  hydrogen 
and  oxygen  (plus  air)  in  a  copper  globe.  He  obtained 


58  HISTORY  OF  CHEMISTRY 

a  blue  liquid  whose  nature  he  was  unable  to  determine. 
The  analyst  whose  aid  he  solicited  showed  him  that  it 
was  a  solution  of  copper  nitrate  in  water.  The  fact  that 
nitric  acid  was  thus  formed  induced  him  to  deny  that 
water  was  a  compound  of  oxygen  and  hydrogen.  In 
the  hands  of  Cavendish,  a  more  thorough  and  careful 
investigator,  this  discovery  led  to  the  demonstration  of 
the  composition  of  nitric  acid. 

Views  as  to  Combustion.  —  He  held  that  all  combus- 
tible substances  contained  hydrogen.  This  was,  in  his 
view,  phlogiston.  The  metals  contained  it  and  their 
calces,  or  oxides,  were  simply  the  metals  deprived  of 
hydrogen.  Thus  he  showed  that  when  iron  oxide  was 
heated  in  hydrogen  gas  the  hydrogen  was  absorbed  and 
metallic  iron  formed.  Rich  iron  slag  was,  in  his  opin- 
ion, iron  with  some  hydrogen  retained.  To  prove  this, 
it  was  mixed  with  the  carbonates  of  the  alkaline  earths 
and  heated  strongly.  This  gave  him  an  inflammable  gas 
and,  according  to  his  belief,  all  inflammable  gases  were 
hydrogen  in  a  more  or  less  impure  condition.  It  was 
later  that  he  discovered  carbon  monoxide  —  also  nitrogen 
dioxide  —  and  he  found  that  water  could  be  impregnated 
with  carbon  dioxide  and  suggested  its  use  in  disease. 


CHAPTER  VIII 

THE  ATOMIC  THEORY 

The  Proposition  of  Lavoisier.  —  The  ground  work  of 
the  new  system  of  chemistry  was  laid  by  Lavoisier  in 
the  following  propositions: 

1.  In  all   chemical  reactions,   only  the  form  of  the 
materials   changes,    the   quantity   remaining   the   same. 
The  substances  used  and  the  products  obtained  can  be 
brought  into  an  algebraic  equation  by  means  of  which 
any  one   unknown   member  may   be   calculated. 

2.  In  all  combustions  the  burning  body  unites  with 
oxygen,  and  in  general  an  acid  is  formed  by  combustion 
of  a  non-metal,  and  a  metallic  calx  is  formed  by  com- 
bustion of  a  metal.     This  calx  is  an  oxide. 

3.  All  acids  contain  oxygen  united  with  a  base  or  a 
radical  which,   in  the  case  of  inorganic  substances,   is 
generally  an  element;    in  organic  substances  it  is  made 
up  of  carbon  and  hydrogen,  and  often  contains  nitrogen 
and  phosphorus  as  well  as  other  elements. 

The  next  stage  in  this  inquiry  into  compounds  and 
combination  concerned  the  method  or  process  of  com- 
bining. What  were  the  combining  particles?  Here  re- 
course to  the  Greek  philosophers  was  once  more  necessary, 
but  sure  and  enduring  foundations  had  to  be  laid  in  sup- 
port of  the  old-world  vision  which  had  been  practically 
lost  sight  of.  A  new  Atomic  Theory  became  a  necessity. 
For  this  we  are  indebted  to  John  Dalton. 

59 


60  HISTORY  OF  CHEMISTRY 

Richter  (1762-1807)  —  It  is  well,  however,  to  refer 
first  to  the  work  of  Richter  who,  through  careful  ana- 
lytical work,  constructed  a  table  giving  the  proportions 
by  weight  in  which  substances  combine.  This  was  a 
distinct  advance  on  the  affinity  tables  which  have  been 
mentioned.  Richter  had  noted  with  keen  interest  that 
one  neutral  salt  could  react  with  another,  and  that  by 
interchange  two  other  neutral  salts  could  be  formed 
without  change  of  reaction  towards  test-papers.  The 
neutrality  was  preserved,  showing  an  equivalence  be- 
tween the  amounts  entering  into  combination.  This 
was  a  most  important  observation,  having  its  bearing 
on  the  law  of  definite  proportions,  and  the  table  of  equiva- 
lents may  be  regarded  as  the  forerunner  of  the  atomic 
weight  table. 

Dalton's  Atomic  Theory.  — John  Dalton  (1766-1844) 
was  more  of  a  mathematician  and  physicist  than  a  chemist. 
Most  of  his  lif e  was  spent  in  Manchester,  England,  as 
instructor  in  mathematics  and  natural  philosophy,  which 
then  included  some  chemistry.  He  was  very  poor,  be- 
ginning to  support  himself  by  teaching  at  twelve  years 
of  age,  and  was  largely  self  taught.  He  was  forced  to 
make  most  of  his  own  apparatus  and  lacked  skill  in 
carrying  out  experiments,  and  in  chemical  manipulation 
fell  far  behind  Priestley.  But  he  excelled  in  logical 
deductions  and  in  generalizations  from  his  facts,  his 
aim  being  the  establishment  of  general,  underlying  laws. 
Priestley  was  a  brilliant  discoverer;  Dalton  a  clear, 
logical,  mathematically  trained  thinker. 

Constitution  of  Mixed  Gases.  —  For  years  he  had  been 
interested  in  meteorological  observations.  Those  which 
he  made  upon  dew  and  aqueous  vapor  existing  in  the 


THE  ATOMIC  THEORY  61 

air  led  him  to  the  publication  in  1801  of  an  important 
paper  upon  the  Constitution  of  Mixed  Gases.  This 
was  followed  by  other  papers  on  the  properties  of  gases 
and  these  prove  that  he  had  formed  the  idea  that  gases 
were  made  up  of  vsniajl^  distinct  particles.  He  wrote  of 
the  pressure  upon  them  and  the  repulsion  between  these 
particles  and  stated  that  "A  vessel  full  of  any  elastic 
fluid  (gas)  presents  to  the  imagination  a  picture  like 
one  full  of  small  shot."  He  reported  the  discovery  of 
some  of  the  fundamental  laws  of  gases.  {First,  there  was 
the  law  of  expansion  by  heat,  according  to  which  all 
gases  independent  of  their  nature  expand  equally  on 
heating.  Another,  the  law  of  partial  pressures,  is  still 
known  as  Dalton's  Law.  He  found  that  the  composition 
of  the  atmosphere  is  the  same  at  low  and  high  temper- 
atures and  that  heavy  gases  diffuse  upward  into  light 
and  light  downward  into  heavy,  thus  forming  always 
a  homogeneous  mixture.  He  noticed  that  water  did 
not  dissolve  all  gases  alike  but  in  amounts  varying  with 
their  nature.  As  this  mattejL  of  solution  was  a  mechan- 
ical operation  in  his  opinion,  he  reached  the  following 
conclusion:  "I  am  persuaded  that  this  circumstance 
depends  upon  the  weight  and  number  of  the  ultimate 
particles  of  the  several  gases,  those  whose  particles  are 
lightest  and  single  being  least  absorbable  and  the  others 
more.  An  inquiry  into  the  relative  weights  of  the  ulti- 
mate particles  is  a  subject,  as  far  as  I  know,  entirely  new." 
He  presented  before  the  Manchester  Literary  and  Phil- 
osophical Society  in  1802  a  paper  which  included  "a 
table  of  the  relative  weights  of  the  ultimate  particles 
of  gaseous  and  other  bodies." 
To  account  for  the  diffusion  of  gases  and  so  complete 


62  HISTORY  OF  CHEMISTRY 

his  vision  of  the  atmosphere,  Dalton  had  to  provide  a 
repulsive  force.  This  he  solved  "  without  letting  in  any 
other  repulsive  force  than  the  well-known  one  of  heat. 
.  .  .  There  was  but  one  alternative  left  —  namely,  to 
surround  every  individual  particle  of  water,  of  oxygen 
and  of  azote  with  heat  and  to  make  them  respectively 
centres  of  repulsion,  the  same  in  a  mixed  state  as  in  a 
simple  state.  .  .  .  Atoms  of  one  kind  did  not  repel  the 
atoms  of  another  kind  but  only  those  of  their  own  kind." 

Of  course,  the  idea  of  the  existence  of  atoms  was  neither 
new  nor  original  with  Dalton.  The  conception  of  the 
Greek  philosophers  was  that:  "The  bodies  which  we 
see  and  handle,  which  we  can  set  in  motion  or  leave  at 
rest,  which  we  can  break  in  pieces  and  destroy,  are  com- 
posed of  smaller  bodies  which  we  cannot  see  or  handle, 
which  are  always  in  motion  and  which  can  neither  be 
stopped  nor  broken  in  pieces,  nor  in  any  way  destroyed 
nor  deprived  of  the  least  of  their  properties." 

Something  of  this  conception  was  held  and  felt  all 
through  the  earlier  days  o£  chemistry.  The  physicists 
Newton  and  Bernouilli  hela  it  (the  latter  believing  the 
pressure  exerted  by  a  gas  upon  the  enclosing  walls  to  be 
due  to  the  constant  bombardment  of  the  atoms),  al- 
though merely  the  term  particle  was  used  by  them  and  by 
Lavoisier,  in  whose  mind  the  same  idea  was  present. 
The  credit  which  belongs  to  Dalton  is  that  he  took  this 
dream  and  by  means  of  collected  facts  and  laws  gave 
it  that  confirmation  which  was  necessary  in  order  that 
it  might  be  ranked  as  a  theory.  While  its  conception 
was  largely  on  physical  reasoning,  the  grounding  which 
brought  general  acceptance  and  established  it  as  a  funda- 
mental theory  of  science  came  when  it  served  as  the  only 


THE  ATOMIC  THEORY  63 

satisfactory   explanation    of   the    fundamental   laws    of 
chemistry.    This  was  also  the  contribution  of  Dalton. 

Law  of  Constant  Proportions.  —  So  far  the  theory 
as  to  the  existence  of  atoms  had  a  physical  rather  than 
a  chemical  basis.  Its  support  came  when  it  was  recog- 
nized as  the  logical  explanation  of  the  basic  laws  of  chem- 
istry. The  first  of  these  was  the  law  of  constant  pro- 
portions, najnelv.  that  in  any  compound  the  relative 
proportions  of  the  constituents  are  definitely  fixed  and 
will  always  be  found  the  same.  This,  one  might  say, 
had  been  tacitly  accepted  by  all  analytical  workers  as 
the  result  of  their  experience  and  a  necessary  basis  for 
their  work.  As  the  number  of  compounds  known  in- 
creased and  analytical  methods  improved  in  accuracy 
some  doubt  arose  as  to  the  fixity  of  these  proportions. 
A  discussion  was  carried  on  for  several  years  between 
two  distinguished  French  chemists,  Berthollet  (1748- 
1822)  and  Proust  (1755-1826),  with  regard  to  the  ex- 
istence of  any  such  regularity,  and  in  the  course  of  it  much 
valuable  analytical  work  wa^done  and  a  number  of  new 
compounds  discovered.  Ims  discussion  aroused  the 
interest  of  the  leading  chemists  of  the  time.  Berthollet 
maintained  that  the  proportions  were  variable  and  noted 
a  number  of  apparent  cases  among  oxides  and  other  com- 
pounds. Proust  showed  that  some  of  these  oxides  con- 
tained hydrogen,  thus  discovering  the  class  of  hydrox- 
ides, and  in  his  analyses  of  the  different  oxides  very  nearly 
arrived  at  the  law  of  multiple  proportions.  One  of  the 
good  results  of  the  controversy  was  to  bring  about  a  clear 
distinction  between,  compounds  and  mixtures.  Ber- 
lost  most  of  his  supporters  before  the  close  of  the 
Another  earnest  supporter  of  the  law  of 


64  HISTORY  OF  CHEMISTRY 

definite  proportions  was  Richter,  though  probably  his 
work  was  unknown  to  Dalton.  He  published  (1792-94) 
the  results  of  his  work  upon  the  proportions  by  weight 
in  various  compounds  under  the  title  of  "A  Foundation 
for  the  Stoichiometry  or  Art  of  Measuring  Chemical 
Elements."  This  is  the  first  work  on  systematic  quan- 
titative analysis.  It  was  a  decade  or  more  before  Rich- 
ter's  excellent  work  received  appropriate  recognition. 
Law  of  Multiple  Proportions.  —  It  has  already  been 
pointed  out  how  the  fact  that  when  two  elements  com- 
bine to  form  a  compound  the  proportion  of  each  is  abso- 
lutely fixed  and  constant  became  firmly  incorporated 
in  the  science  and  a  recognized,  even  if  unstated,  law. 
This  to  the  seeing  eye  meant  a  combining  of  atom  with 
atom,  though  sometimes  it  might  mean  a  greater  number 
of  atoms,  provided  this  number  was  always  the  same. 
There  is  another  law  where  the  call  for  discrete  par- 
ticles of  fixed  weight  is  still  clearer.  With  these  two  funda- 
mental laws  there  was  an  assured  basis  for  Dalton's 
theory  of  the  existence  ^  unchanging  atoms.  This 
second  law  is  known  as  tlrelaw  of  multiple  proportions 
and  was  discovered  and  announced  by  Dalton  himself. 
The  careful  analytical  work  of  Proust  and  Berthollet 
and  others  gave  him  the  necessary  facts  for  his  general- 
ization. Considering  these  facts,  he  found  that  when 
two  elements  combined  to  form  one  compound  there  were 
certain  definite  proportions  in  which  they  united.  If 
they  formed  more  than  one  compound,  under  changed 
conditions,  then  the  proportion  of  one  progressed  by 
regular  increments,  an  increase  of  once  or  twice  the  first 
proportion  or  some  simple  multiple  of  it.  For  this  he 
that  his  hypothesis  of  atoms  gave  a  plausible  explani 


THE  ATOMIC  THEORY  65 

—  and  the  only  plausible  one  —  the  increase  correspond- 
ing with  a  doubling,  trebling,  etc.,  of  the  weight  of  the 
original  atom.  It  was  this  that  immediately  attracted 
the  attention  of  the  leading  chemists.  Many  set  out  to 
test  the  truth  of  the  law  and  with  its  establishment 
the  case  was  won. 

Dalton  told  his  theory  to  Thomson,  a  noted  chem- 
ist who  was  the  author  of  some  of  the  leading  text-books 
of  his  day.  Thomson  published  Dalton's  views  in  his 
System  of  Chemistry  in  1807.  Sir  Humphry  Davy 
opposed  the  new  hypothesis,  but  was  won  over  to  it  and 
so  were  W0^as^on  an(^  others,  though  they  saw  difficul- 
ties in  its  application  which  greatly  delayed  its  general 
acceptance.  The  essential  parts  of  Barton's  theory  can 
be  put  in  two  sentences: 

1.  Every  element  is  made  up  of  similar  atoms  of  con- 
stant weight. 

2.  Chemical  compounds  are  formed  by  the  union  of 
the  atoms  of  the  different  elements  in  simple  numerical 
relations. 

All  analytical  work  has  been  based  on  these  two  as- 
sumptions and  the  results  have  confirmed  them.  Dalton 
further  speculated  on  the  nature  of  the  atoms,  regard- 
ing them  as  spheres  surrounded  by  an  atmosphere  of 
heat,  not  touching  one  another  but  in  constant  motion. 

Determining  the  Weights  of  the  Atoms.  —  If  the 
atomic  theory  were  a  true  explanation  of  the  facts  of 
chemical  combination,  then  its  first  and  most  important 
application  would  lie  in  a  determination  of  the  relative 
weights  of  the  atoms  of  the  various  elements.  This 
might  be  arrived  at  by  a  determination  of  the  combin- 
ing proportions  entering  into  different  compounds, 


66  HISTORY  OF  CHEMISTRY 

provided  the  number  of  atoms  in  such  compounds  were 
known.  Now  it  was  in  this  that  the  supporters  of  the 
theory  met  their  first  and  greatest  difficulty.  By  what 
possible  means  could  the  number  of  the  constituent 
atoms  in  a  compound  be  accurately  known? 

Dalton's  Rules.  —  Following  up  his  conception  of 
the  existence  of  atoms  Dalton  began  to  determine  their 
relative  weights,  taking  for  his  standard  or  unit  hydro- 
gen, the  lightest  of  them.  A  list  of  these  weights  as  deter- 
mined by  him  was  published  in  1805.  They  show  very 
faulty  work  and  were  superseded  later  by  the  remark- 
ably accurate  results  obtained  by  Berzelius.  These 
weights  as  given  by  Dalton  seem  to  have  come  very 
slightly  into  use.  To  overcome  the  difficulty  of  telling 
how  many  atoms  entered  into  combination  to  form  a 
particle  of  any  compound,  he  adopted  some  very  arbi- 
trary rules  which  were  afterwards  shown  to  be  without  just 
basis.  These  rules  had  the  merit  of  simplicity,  how- 
ever, and  were  about  the  best  that  could  be  formulated 
at  that  time.  First,  he  divided  compounds  into  binary, 
ternary,  quaternary,  etc.,  according  -as  they  contained 
two,  three,  four,  or  more  atoms.  Then  he  adopted  the 
following  rules : 

1.  When  only  one  combination  of  two  bodies  can  be 
obtained  it  must  be  presumed  to  be  a  binary  one  unless 
some  cause  appear  to  the  contrary. 

2.  When  two  combinations  are  observed  they  must 
be  presumed  to  be  a  binary  and  a  tertiary. 

3.  When   three   combinations   are   obtained   we  may 
expect  one  to  be  a  binary  and  the  other  two  tertiary. 

4.  When  four  combinations  are  observed  we  should 
expect  one  binary,  two  ternary,  and  one  quaternary,  etc. 


THE  ATOMIC  THEORY  67 

How  simple  the  whole  matter  would  be  if  nature  always 
chose  the  simplest,  plainest  paths!  But  happily  for  our 
development,  she  often  has  a  confusing  way  of  leading 
into  many  by-paths.  Besides  this  difficulty  as  to  the 
number  of  atoms,  Dalton's  use  of  the  term  atom  was 
often  misleading.  He  made  little  distinction  between 
the  ultimate  particles  of  elements  or  of  compounds  or 
the  ideal  indivisible  atom.  This  was  a  most  serious 
flaw.  It  caused  Dalton  himself  to  reject  the  work  of 
Gay-Lussac;  and  it  caused  others,  seeing  these  incon- 
sistencies, to  hesitate  to  accept  Dalton's  views.  Two 
things  were  much  needed  —  a  clearer  definition  of  atoms 
and  some  reliable  method  of  determining  the  number  of 
atoms  in  a  compound  particle. 

Gay-Lussac  (1778-1850). —  The  latter  problem  was 
partially  solved  by  the  labors  of  Gay-Lussac.  This  dis- 
tinguished pupil  of  Berthollet  was  a  well-trained  chem- 
ist, capable  of  very  accurate  analytical  work  and  pos- 
sessing scientific  acumen  in  a  very  high  degree.  He 
enriched  chemical  literature  by  many  excellent  investi- 
gations, working  often  in  company  with  Thenard,  Hum- 
bolt,  and  Liebig.  His  most  noteworthy  work  was  upon 
iodine,  cyanogen  (the  first  compound  radical),  the  alka- 
line oxides,  the  isolation  of  boron,  improved  methods 
for  organic  analysis,  and  many  similar  studies. 

Law  of  Volumes.  —  His  name  is  especially  associated 
with  his  researches  upon  the  combining  volumes  of  gases. 
He  discovered  the  law  of  the  expansion  of  gases  under 
the  influence  of  equal  temperature  increments.  He  also 
studied  the  combining  volumes  of  gases  and  deduced 
from  his  experiments  the  law  of  volumes  for  gases.  This 
law  of  volumes  may  be  stated  thus :  The  volumes  in  which 


68  HISTORY  OF  CHEMISTRY 

two  gases  combine  bear  a  simple  ratio  to  one  another 

and  to  the  volume  of  the  resulting  gaseous  product.    Thus 

one  volume  of  oxygen  always  reacts  with  two  volumes 

of  hydrogen  to  form  two  volumes  of  steam.    Any  excess 

of  either  oxygen  or  hydrogen  will  be  left  over.    So  also, 

x-one  volume  of  nitrogen  unites  with  exactly  three  vol- 

\umes  of  hydrogen  and  two  volumes  of  ammonia  result. 

T,  j  The  account  of  his  work  and  the  conclusions  he  drew 

(from  it   were   given   in   1808. 

Objections  to  the  Law.  —  Gay-Lussac  was  well  ac- 
quainted with  Dalton's  hypothesis  and  showed  in  part 
how  his  discoveries  accorded  with  it.  A  similar  molecu- 
lar condition  was  essential  in  order  that  all  gases  should 
behave  alike  towards  pressure  and  changes  of  tempera- 
ture, and,  in  addition,  obey  his  law  of  volumes.  In  other 
words,  equal  volumes  of  gases  must  contain  equal  num- 
bers of  molecules.  Gay-Lussac  made  no  distinction  be- 
tween these  molecules  and  atoms,  recognizing  but  one 
kind  of  final  particle.  Dalton  took  exception  to  this 
reasoning,  and  in  his  reply  said  that  he  too  had  once 
held  the  same  idea  as  to  combining  volumes  but  had 
seen  that  it  was  untenable.  He  further  maintained  that 
the  experiments  of  Gay-Lussac  were  inaccurate  and  that 
the  gases  did  not  combine  exactly  by  volumes  but  often 
by  fractions  of  volumes.  His  argument  may  be  illustrated 
best  by  taking  some  substance,  as  hydrochloric  acid, 
as  an  example.  One  atom  of  hydrogen  chloride  consists 
of  one  atom  of  chlorine  and  one  atom  of  hydrogen.  On 
combination  of  equal  volumes  of  these  two  gases,  there- 
fore, there  should  result  but  one  volume  of  hydrogen 
chloride  if  the  supposition  that  equal  volumes  of  gases 
contain  equal  numbers  of  final  particles  is  correct.  On 


THE  ATOMIC  THEORY  69 

the  contrary,  the  yield  is  two  volumes  of  hydrogen  chlo- 
ride. If  these  final  particles  were  atoms,  then  the  result- 
ing volumes  of  hydrogen  chloride  must  each  contain 
only  half  as  many  particles  as  the  volumes  of  the  com- 
bining gases  or  the  hydrogen  chloride  is  made  up  of  half- 
atoms  of  hydrogen  and  chlorine.  This  reasoning  is 
manifestly  final  so  far  as  the  theory  of  the  volumes  con- 
taining the  same  number  of  atoms  is  concerned  unless 
some  different  definition  of  atoms  is  assumed. 

Avogadro's  Theory.  —  The  solution  of  the  difficulty 
was  shown  by  Avogadro  (1776-1856)  in  1811.  This 
Italian  physicist  made  a  distinction  between  two 
kinds  of  ultimate  particles  which  we  know  as  molecules 
and  atoms.  The  molecules  were  compound  particles 
and  were  made  up  of  the  indivisible  atoms.  In  hydrogen 
gas,  therefore,  we  have  as  the  final  particles  molecules, 
each  made  up  of  two  atoms  of  hydrogen;  and  a  molecule 
of  oxygen  is  made  up  of  two  atoms  of  oxygen  and  chlo- 
rine has  two  atoms  to  the  molecule.  With  this  hy- 
pothesis the  volume  relations,  as  given  by  Gay-Lussac, 
become  entirely  regular  and  intelligible.  These  dis- 
coveries of  Avogadro  have  been  sometimes  credited  to 
the  French  physicist  Ampere,  but  his  statement  appeared 
three  years  later  (1814)  and  lacks  the  clarity  and  full- 
ness of  that  of  Avogadro.  He  assumed  the  presence  of 
four  atoms  instead  of  two  in  the  molecules  of  elementary 
gases  and  attempted  to  extend  his  hypothesis  to  the 
constitution  of  molecules  existing  in  solids.  His  mem- 
oir first  appeared  in  the  form  of  a  letter  to  Berthollet 
and  he  showed  in  it  his  ignorance  of  the  work  of  Avo- 
gadro. 


CHAPTER  IX 

THE    ATOMIC  WEIGHTS 

Taking  hydrogen  as  the  unit,  Dalton  determined  a 
small  number  of  atomic  weights  but,  lacking  skill  as  a 
chemist,  his  results  were  so  faulty  as  to  cause  much  un- 
certainty with  regard  to  the  whole  matter.  Other  chem- 
ists took  up  this  task  with  greater  success.  Chief  among 
these  was  Berzelius,  who  in  conjunction  with  his  pupils 
undertook  the  determination  of  the  atomic  weights  of 
all  the  known  elements.  The  analytical  work,  of  course, 
greatly  excelled  that  of  Dalton  and  in  the  rules  laid 
down  for  his  guidance  in  deciding  the  number  of  atoms 
in  a  given  compound  or  molecule  his  intimate  knowl- 
edge of  the  chemical  behavior  of  many  substances,  his 
acuteness  of  observation,  his  attention  to  the  smallest 
details,  and  his  painstaking  patience  render  his  work 
truly  remarkable.  Many  of  his  atomic  weights  are 
still  quoted  and  made  use  of  in  settling  these  physical 
constants  over  which  chemists  have  been  busied  for 
so  long  a  time.  His  standard  was  oxygen  taken  as  100. 
Still  he  was  at  a  loss  for  a  reliable  method  of  telling  how 
many  atoms  there  were  in  the  molecules  with  which  he 
dealt,  and  his  rules  for  settling  this  question  were  in 
some  respects  arbitrary  and  unsatisfactory.  As  knowl- 
edge grew  and  new  aids  were  discovered  for  arriving 
at  the  number  of  atoms  in  a  molecule,  he  availed  him- 
self of  them  and  corrected  his  tables  of  the  atomic  weights 

70 


THE  ATOMIC  WEIGHTS  71 

which  he  issued  every  now  and  then  through  a  number 
of  years. 

The  Standard  for  the  Atomic  Weights.  —  Since  the 
atomic  weights  are  necessarily  relative  to  that  of  some 
one  elementary  atom  taken  as  the  unit  or  standard, 
it  is  essential  that  the  standard  shall  be  the  best  avail- 
able and  universally  recognized  as  such.  The  standard 
has  been  changed  several  times  since  Dalton  chose  hy- 
drogen, the  lightest  known  atom,  and  assigned  to  it  the 
unit  value.  Hydrogen,  however,  forms  comparatively 
few  compounds  with  the  other  elements  and  that  means 
that  in  most  cases  the  relative  value  could  be  determined 
only  indirectly.  A  little  later  Wollaston  chose  oxygen, 
giving  it  the  value  one.  This  had  the  disadvantage  of 
giving  fractional  values  for  several  of  the  atomic  weights. 
It  was  probably  to  avoid  this  that  Berzelius,  when  he 
chose  oxygen  for  his  standard,  assigned  it  the  value  100. 
Oxygen  was  chosen  because  of  the  large  number  of  com- 
pounds which  it  formed  and  hence  the  possibility  of 
direct  determinations.  Under  this  system  some  of  the 
atomic  weights  were  inconveniently  large,  running  over 
one  thousand.  Some  years  later  hydrogen  was  restored 
(largely  through  the  influence  of  Gmelin)  to  its  position 
as  standard  with  the  value  1  and  held  this  position  until 
near  the  close  of  the  nineteenth  century.  In  the  early 
part  of  the  last  decade  of  that  century  the  prolonged 
discussion  came  to  an  end  by  the  general  adoption  of 
oxygen  as  the  standard  with  the  value  16  and  the  ap- 
pointment of  an  international  committee  which  was 
to  have  charge  over  all  corrections  in  the  atomic  weights 
and  issue  annually  tables  containing  all  revisions  accepted 
by  them. 


72  HISTORY  OF  CHEMISTRY 

Wollaston's  Equivalents.  —  The  uncertainty  connected 
with  the  atomic  weights  as  determined  under  Dalton's 
rules,  or  indeed  under  any  arbitrary  method  of  proce- 
dure, led  Wollaston,  his  fellow  countryman,  to  suggest 
abandoning  the  use  of  the  term  atom  and  substituting 
that  of  equivalent.  This  term  he  adopted  from  the  work 
of  Richter.  Wollaston  meant  by  it  the  relative  quanti- 
ties or  proportions  in  which  bodies  unite,  thus  doing 
away  with  the  idea  of  atoms.  He  hoped  in  this  way  to 
escape  all  question  as  to  the  number  of  atoms  in  a  com- 
pound. It  is  easy  to  see  that  his  method  rather  increased 
than  diminished  the  complications,  and  the  atomic  theory, 
which  was  based  on  fundamental  laws,  was  to  be  done 
away  with  because  of  difficulties  in  settling  their  weight. 
Still  the  desire  to  eliminate  theory  was  strong  and  many 
chemists,  especially  the  English,  continued  to  use  the 
term  equivalent  for  many  decades  after  the  time  of 
Wollaston.  The  difficulties  will  be  seen  if  examples  are 
taken.  Using  Wollaston's  standard  of  oxygen  equal 
to  1,  we  find  there  are  two  compounds  with  carbon. 
One  gives  the  ratio  of  carbon  to  oxygen  as  0.75  to  1; 
the  second  gives  the  ratio  of  0.375  to  1.  Which  ratio 
shall  be  taken?  If  the  least  equivalent  is  taken,  then 
what  is  the  other?  Manifestly  the  knowledge  of  the 
number  of  the  particles  in  the  compound  is  just  as  essen- 
tial for  equivalents  as  for  atoms. 

Law  of  Specific  Heats.  —  In  the  year  1819  Dulong 
and  Petit,  while  experimenting  upon  the  specific  heats 
of  the  metals  and  other  substances,  came  upon  the  im- 
portant truth  that  these  were  very  nearly  inversely 
proportional  to  their  atomic  weights.  Multiplied  by  their 
atomic  weights  they  gave  a  constant  quantity  which  is 


THE  ATOMIC  WEIGHTS  73 

called  the  atomic  heat.  The  law  as  stated  by  the  authors 
is:  The  atoms  of  the  different  elements  have  the  same 
capacity  for  heat.  It  is  possible,  therefore,  by  means 
of  the  specific  heat  to  approximate  the  true  atomic  weight 
and  arrive  at  a  decision  as  to  which  of  two  or  more 
possible  figures  represent  the  correct  weight. 

There  were  exceptions  to  the  law  which  were  explained 
later.  Still  the  law  was  extended  to  simple  chemical 
compounds  and  proved  of  use  after  it  was  more  fully 
understood.  Berzelius  opposed  the  acceptance  of  it  at 
first,  partly  because  it  would  necessitate  a  revision  of 
his  table  of  atomic  weights  and  might  endanger  accepted 
views  as  to  the  atomic  relations.  He  gradually  gave  up 
this  stand  when  the  law  was  confirmed  by  other  workers 
and  determinations  more  accurate  than  the  first  ones 
of  Dulong  and  Petit  were  made  of  the  specific  heats. 

Isomorphism.  —  In  the  same  year  Mitscherlich  an- 
nounced what  was  called  the  law  of  isomorphism.  While 
engaged  in  a  research  upon  the  salts  of  phosphoric  and 
arsenic  acids,  he  reached  the  conclusion  that  compounds 
of  analogous  composition  and  containing  the  same  number 
of  atoms  crystallize  in  the  same  form  or,  in  other  words, 
are  isomorphous.  For  this  to  be  really  useful  in  deter- 
mining atomic  weights  it  was  necessary  to  reverse  it  and 
to  have  it  hold  true  that  isomorphous  compounds  were 
analogous  and  contained  the  same  number  of  atoms^ 
Here  many  difficulties  presented  themselves,  necessi- 
tating narrower  and  narrower  definitions  of  isomorphism. 
It  is  evident  that  though  analogy  or  similarity  of  crys- 
tal form  may  have  a  bearing  upon  the  molecular  composi- 
tion and  arrangement,  we  are  as  yet  unable  to  determine 
fully  this  bearing.  Berzelius  took  up  the  discovery  of 


74  HISTORY  OF  CHEMISTRY 

Mitscherlich  with  enthusiasm  and  made  frequent  use 
of  it  in  testing  his  atomic  weights. 

Electro-chemical  Equivalents.  —  Mention  should  be 
made  in  this  connection  of  Faraday's  law.  This  was 
deduced  from  his  experiments  in  1834  on  the  dissociat- 
ing action  of  the  electric  current  upon  electrolytes.  In 
decomposing  different  electrolytes  such  as  water,  metallic 
chlorides,  etc.,  he  found  that  there  separated  at  the 
positive  or  negative  electrodes  equivalent  amounts  of 
respective  constituents,  provided  the  same  quantity  of 
electricity  were  used.  The  amounts  separated  were  called 
the  electro-chemical  equivalents.  The  intensity  of  the 
current  needed  to  bring  about  the  decomposition  he  re- 
garded as  a  measure  of  the  force  of  affinity.  Faraday 
thought  that  the  determination  of  these  equivalents 
would  prove  a  valuable  aid  to  the  correct  determina- 
tion of  the  atomic  weights.  The  application  of  this 
method  is  to  a  certain  extent  limited  but  it  has  been 
used  in  some  recent  accurate  determinations. 

Work  of  Dumas  on  the  Atomic  Weights.  —  In  their 
work  upon  the  atomic  weights  Dumas  and  other  French 
chemists  made  especial  use  of  the  law  of  volumes  as 
given  by  Gay-Lussac  and  adopted  the  distinction  made 
by  Avogadro  between  atoms  and  molecules.  The  equiva- 
lents suggested  by  Wollaston  were  rejected  by  them  as 
Applicable  only  to  a  limited  range  of  substances,  such  as 
acids  and  bases,  besides  being  indefinite  or  not  deter- 
minable  when  identified  with  combining  weights,  since 
many  substances  united  in  several  different  proportions 
to  form  compounds.  Some  of  Dumas'  determinations, 
as  those  of  phosphorus,  tin,  and  silicon,  show  that  he 
did  not  realize  the  full  importance  of  Avogadro's  theory 


THE  ATOMIC  WEIGHTS  75 

as  an  aid  in  such  determinations.  Still  he  believed  that 
this  theory  gave  a  surer  basis  for  solving  such  questions, 
and  drew  up  a  table  of  atomic  weights  making  use  of 
it  and  the  law  of  Dulong  and  Petit.  He  used  the  term 
elementary  molecules  and  said  that  there  was  no  means 
of  deciding  how  many  smallest  particles  these  mole- 
cules contained.  In  accuracy  and  correctness  his  work 
fell  below  that  of  Berzelius. 

Vapor  Densities.  —  Dumas  devised  an  accurate  and 
excellent  method  for  determining  the  specific  gravities, 
or  densities,  of  gases  which  could  be  used  at  high  temper- 
atures, thus  enabling  him  to  experiment  upon  the  vapor 
densities  of  iodine,  phosphorus,  sulphur,  mercury,  etc. 
His  results,  instead  of  confirming,  tended  rather  to  dis- 
prove the  law  of  volumes.  The  trouble  lay  in  the  com- 
plex nature  of  the  molecules  experimented  upon,  but  of 
course  this  was  unknown  to  Dumas.  He  finally  de- 
clared that  even  in  the  case  of  the  simple  gases  like  vol- 
umes did  not  contain  equal  numbers  of  chemical  atoms. 
Berzelius  also  had  been  practically  forced  to  give  up 
the  law  of  volumes,  at  least  so  far  as  any  use  in  atomic 
weight  determinations  was  concerned,  limiting  its  appli- 
cation to  the  uncondensed  or  so-called  permanent  gases. 

Chemists  therefore  looked  with  indifference  or  dis- 
favor on  this  law  which  is  the  mainstay  of  modern  work 
upon  the  atomic  weights.  The  law  of  Dulong  and  Petit 
was  also  shown  to  have  some  notable  and  unexplained 
exceptions,  and  Mitscherlich  by  his  further  discovery 
of  dimorphism  had  thrown  much  doubt  upon  his  law  of 
isomorphism.  So  at  the  close  of  the  thirtieth  year  of  the 
nineteenth  century  the  atomic  theory  was  regarded  by 
many  chemists  as  relegated  to  a  hypothetical  position. 


76  HISTORY  OF  CHEMISTRY 

Gmelin's  Views.  —  Some  took  up  again  the  equivalents 
of  Wollaston.  Certainly  little  distinction  was  made  be- 
tween these  and  the  atoms  of  Dalton,  and  the  dualistic 
system  of  Berzelius  lost  ground.  Gmelin,  the  author 
of  the  most  complete  handbook  or  encyclopedia  of  chem- 
istry up  to  his  time,  and  the  most  influential  as  it  went 
through  many  editions  and  formed  the  basis  subsequently 
of  Watts'  Dictionary  of  Chemistry,  was  the  leader  in  this 
new  school  of  chemistry.  In  the  edition  of  his  handbook 
published  at  this  time,  the  fourth  decade,  he  gave  up  the 
atomic  theory  altogether.  He  recognized  no  difference 
between  chemical  compounds  and  mixtures.  Two  sub- 
stances, according  to  his  ideas,  could  combine  in  an  un- 
ending number  of  proportions.  In  the  case  of  a  strong 
affinity  between  them  the  tendency  was  toward  a  limita- 
tion to  a  few  proportions.  To  each  substance  then  a 
sort  of  mixing  weight  could  be  assigned  and  this  number 
could  be  used  in  analytical  calculations.  His  table  of 
equivalents  halved  most  of  the  atomic  weights.  Thus, 
H  =  1,  O  =  8,  S  =  16,  C  =  6,  etc.  Water  became  HO. 
The  rule  was  to  make  everything  conform  to  the  utmost 
simplicity.  Where  there  was  choice  between  several 
possible  equivalents  for  any  one  element  he  took  the 
the  least  and  simplest.  These  numbers  and  formulas 
were  retained  by  many  chemists  for  some  decades  after- 
wards. 

Confusion  in  the  Sixth  Decade.  —  The  middle  of  the 
century  saw  the  condition  of  affairs  regarding  these 
physical  constants  a  badly  mixed  one.  Two  units  or 
standards  were  in  use.  Dalton  had  used  hydrogen  as 
the  unit  and  this  was  adopted  by  Gmelin  and  many 
others.  Wollaston  and  Berzelius  took  oxygen  as  the 


THE  ATOMIC  WEIGHTS  77 

standard,  Wollaston  giving  it  the  value  10  and  Ber- 
zelius  using  the  value  100,  while  Thomson  gave  it  the 
value  1.  But,  far  worse  than  having  two  standards, 
widely  differing  values  were  assigned  for  the  atomic 
weights  and  all  needed  revision.  In  Germany,  for  in- 
stance, the  value  for  carbon  was  6  and  for  oxygen  8. 
In  France  these  values  were  respectively  3  and  8. 

Revisions  of  the  Atomic  Weights.  —  Dumas  was  es- 
pecially active  in  the  revision  of  these  numbers.  His 
determination  of  the  atomic  weight  of  carbon  and  his 
work,  in  conjunction  with  Boussingault,  to  determine 
the  ratio  of  hydrogen  to  oxygen  in  water  are  classical. 
Dumas  fixed  the  number  16  for  oxygen.  The  exact  re- 
sult was  15.96.  This  ratio  has  been  the  subject  of  more 
painstaking  and  careful  determinations  than  any  other 
in  chemistry,  yet  without  complete  accord.  Dumas 
also  determined  many  other  atomic  weights.  Others 
taking  part  in  this  work  of  revision  were  Erdmann,  Mar- 
chand,  Marignac,  De  Ville,  and  Scheerer,  but  easily 
the  greatest  of  them  all  in  care  and  accuracy  was  Stas. 
His  work  was  monumental  in  the  pains  taken  to  secure 
absolute  accuracy,  and  yet  in  a  few  years  errors  were 
found  and  the  so-called  Dumas  correction,  as  well  as 
others,  had  to  be  applied  to  the  numbers  found  by  him. 
The  atomic  weights  determined  by  him  with  the  great- 
est care  were  those  of  silver,  potassium,  sodium,  lith- 
ium, lead,  chlorine,  bromine,  iodine,  sulphur,  and  ni- 
trogen. 

Clearing  up  the  Confusion.  —  The  solving  of  the 
problems  which  confronted  those  devoting  their  atten- 
tion to  the  atomic  weights  and  the  clearing  up  of  the 
existing  confusion  were  in  great  measure  brought  about 


78  HISTORY  OF  CHEMISTRY 

through  the  development  of  organic  chemistry.  Much 
light  was  thrown  upon  the  distinction  between  atoms 
and  molecules  and  the  dominant  doctrine  in  this  branch 
of  chemistry  quietly  assumed  the  truth  of  Dalton's  theory 
in  all  its  important  particulars  as  the  only  satisfactory 
explanation  of  and  adequate  basis  for  the  work  done. 
Frankland's  researches  on  the  organo-metallic  substances 
practically  did  away  with  the  old  confusion  between 
atoms  and  molecules.  Then,  too,  the  value  of  Avo- 
gadro's  law  as  an  aid  to  the  correct  determinations  of 
atomic  weights  became  more  fully  recognized  and  lab- 
oratory methods  were  more  accurate.  This  was  notably 
the  case  in  vapor  density  determinations.  Much  credit 
for  placing  atomic  weight  work  upon  a  more  satisfactory 
basis  is  due  to  Cannizzaro.  In  1856  he  published  a  small 
pamphlet  in  which  he  took  a  determined  stand  upon  the 
necessity  for  the  use  of  the  means  already  at  hand  and 
especially  the  theory  of  Avogadro  that  equal  volumes  of 
gases  contained  equal  numbers  of  particles.  In  1860  a 
meeting  was  called  at  Karlsruhe  by  distinguished  chem- 
'ists  of  various  nationalities  to  see  if  some  general  agree- 
ment could  not  be  reached  as  to  standards,  atomic  weights, 
and  chemical  notation.  The  meeting  was)presided  over 
by  Dumas.  No  general  agreement  was  reached  but 
Cannizzaro's  pamphlet,  in  which  he  urged  chemists  to 
place  reliance  in  the  methods  mentioned  and  so  to  cor- 
rect many  of  the  false  atomic  weights  then  in  use,  was 
distributed  towards  the  close  of  the  meeting.  His  argu- 
ments proved  convincing,  resulting  in  the  general  adop- 
tion of  the  modern  methods. 

Constancy   of   the   Atomic   Weights.  —  The  question 
has  repeatedly  arisen  as  to  whether  the  atomic  weights 


THE  ATOMIC  WEIGHTS  79 

are  variable  within  narrow  limits.  The  approximate 
agreement  of  the  best  determinations  would  tend  to 
exclude  any  other  than  a  slight  variation.  This  ques- 
tion Stas  proposed  for  himself  before  starting  upon  his 
classic  work  on  the  atomic  weights.  The  conclusion 
he  drew  from  his  experiments  was  that  they  were  un- 
changeable. The  question  was  raised  again  by  Schiitz- 
enberger  and  Butlerow.  These  chemists  supposed  the 
range  of  variation  to  be  very  slight  yet  distinctly  to  be 
detected  by  analysis.  Vogel  also  came  to  the  conclusion 
that  the  atomic  weights  vary  because  those  found  by  the 
use  of  certain  compounds  differ  from  those  derived 
from  other  compounds.  If  this  assumption  is  correct, 
then  the  law  of  conservation  of  mass  and  along  with  it  that 
of  constancy  of  proportions  cease  to  fall  under  the  cate- 
gory of  laws. 

In  1906  Landolt  put  the  law  of  conservation  of  mass 
to  a  critical  test.  A  vessel  was  so  arranged  that  two 
substances  could  be  accurately  weighed  and  then  re- 
action allowed  to  take  place  between  them  without  any 
possible  loss  of  substance.  A  large  number  of  experi- 
ments were  carried  out  with  every  refinement  as  to  ap- 
paratus. The  second  weighing  revealed  a  difference  of 
about  one  part  in  10,000,000.  Such  differences  do  not 
exceed  the  unavoidable  experimental  error. 

A  number  of  years  ago  Crookes  suggested  that  one 
might  assume  the  presence  of  a  few  of  what  he  called 
"worn  atoms"  in  the  countless  numbers  of  others  which 
must  come  under  consideration  in  any  atomic  weight 
determination.  Essentially,  this  means  the  presence  of 
atoms  of  the  same  element  which  vary  slightly  in  weight 
and  mass.  The  presence  of  a  few  such  atoms  would  es- 


80  HISTORY  OF  CHEMISTRY 

cape  detection  as  falling  within  the  experimental  error. 
Within  the  past  few  years  the  theory  of  isotopes  has 
grown  up  and  it  seems  certain  that  such  isotopes  exist. 
In  the  case  of  gases  they  may  be  separated  by  the  dif- 
fusion process.  First,  an  isotopic  neon  atom  was  dis- 
covered, then  hydrogen,  chlorine,  and  others.  These 
isotopes  bear  a  very  small  ratio  to  the  total  number  of 
atoms  present  in  any  given  volume. 


CHAPTER  X 

NATURE  OF  THE  ATOM 

It  is  worthy  of  note  that  from  the  very  beginning  the 
modern  atomic  theory  laid  little  or  no  stress  upon  the 
indivisibility  of  the  elementary  atom.  For  all  purposes 
of  the  chemist  it  was  sufficient  to  know  that  under  all 
manipulations  and  changes  in  the  laboratory  or  in  nature 
it  seemed  to  remain  intact  and,  therefore,  could  be  as- 
sumed as  an  ultimate  particle  so  far  as  experience  went. 
Within  a  decade  after  the  announcement  of  the  theory 
there  sprang  up  a  hypothesis  as  to  the  possible  com- 
pound nature  of  the  atom  and  hence  its  origin  or  gene- 
sis. This  was  the  well-known  Prout's  hypothesis  which 
was  announced  in  1815. 

Prout's  Hypothesis.  —  This  hypothesis  was  based  on 
the  assumption  that  all  the  atomic  weights  were  whole 
numbers  and,  therefore,  multiples  of  the  unit  hydrogen. 
From  this  Prout  reasoned  that  these  elements  were 
only  different  grades  of  condensation  of  hydrogen,  which 
was,  therefore,  the  primal  element.  No  additional  proofs 
were  suggested  in  support  of  this  theory.  Prout,  the 
author  of  it,  was  a  physician  and  did  little  chemical 
work  of  value.  Even  if  the  atomic  weights  had  been 
all  whole  numbers  this  was  in  itself  no  proof  that  they 
were  made  up  of  hydrogen.  Yet  this  hypothesis  proved 
to  be  an  attractive  one  to  many  chemists.  As  the  years 
the  increasingly  accurate  determinations  showed 
81 


82  HISTORY  OF  CHEMISTRY 

that  some  of  the  atomic  weights  were  not  whole  numbers 
and  that  the  fractions  persisted,  though  improved  work 
might  vary  them  slightly. 

Views  of  Berzelius.  —  Berzelius  regarded  the  hypoth- 
esis with  favor  when  first  brought  to  his  attention. 
He  soon  became  its  first  and  strongest  antagonist.  In 
1825  he  published  a  table  of  the  atomic  weights  which 
contained  a  number  of  fractions  and  he  protested  strongly 
against  the  practice  of  rounding  off  these  fractions  into 
whole  numbers.  As  Hoffman  says,  "He  could  not  per- 
suade himself  that  the  numerical  relations  of  these  val- 
ues betokened  an  inner  connection  of  the  elements  nor 
yet  a  common  origin.  On  the  contrary,  he  was  of  the 
opinion  that  these  apparent  relations  would  disappear 
more  and  more  as  these  values  were  more  accurately 
determined.  For  him,  therefore,  there  existed  as  many 
forms  of  matter  as  there  were  elements;  in  his  eyes 
the  molecules  of  the  various  elements  had  nothing  in 
common  with  one  another  save  their  immutability  and 
their  eternal  existence."  Our  later  knowledge  of  these 
matters  would  tend  to  show  that  in  this  Berzelius  had 
gone  too  far  to  the  other  extreme. 

Testing  the  Hypothesis.  —  In  1832  Turner  was  spe- 
cially delegated  by  the  British  Association  to  investi- 
gate this  question.  If  barium,  chlorine,  etc.,  really  had 
fractional  atomic  weights  then  the  hypothesis  in  its 
original  form  was  untenable.  Turner's  results  were 
adverse  to  the  hypothesis.  So  also  were  Penny's.  Mar- 
ignac  suggested  that  if  half  the  atomic  weight  of  hydro- 
gen were  taken  then  all  known  atomic  weights  would 
be  multiples  of  it.  The  idea  was  taken  up  by  Dumas 
with  enthusiasm  but  he  found  this  factor  must  be  once 


NATURE  OF  THE  ATOM  83 

more  halved,  so  one-fourth  the  hydrogen  atom  was 
taken.  It  is  not  quite  clear  why  this  was  not  a  begging 
and  abandonment  of  the  whole  question.  But  the  very 
careful  and  accurate  work  of  Stas  upon  the  atomic  weights 
made  even  this  position  impossible.  And  so  the  factor 
was  by  some  shifted  to  one-tenth  the  unit  and  by  Zan- 
gerle  to  the  one-thousandth  part  of  the  hydrogen  atom. 
With  this  it  passed  the  limit  of  experimental  evidence 
and  lost  all  weight  and  meaning. 

Numerical  Relations  between  the  Atomic  Weights.  — 
The  first  numerical  regularities  observed  between  the 
atomic  weights  were  the  triads  of  Dobereiner.  This 
chemist  seems  to  have  observed  first  that  the  combin- 
ing weight  of  strontium  was  the  arithmetical  mean  of 
those  of  calcium  and  barium.  A  like  regularity  was 
noted  with  regard  to  certain  physical  properties  of  these 
elements  and  some  of  their  compounds.  This  led  him 
for  a  while  to  question  the  independent  existence  of 
strontium.  Several  similar  triads  were  discovered  among 
the  other  elements  as  lithium,  sodium,  and  potassium; 
chlorine,  bromine,  and  iodine;  sulphur,  selenium,  and 
tellurium.  He  was  careful  not  to  let  this  grouping  depend 
upon  the  atomic  weights  alone  but  insisted  that  only 
elements  exhibiting  decided  analogies  of  properties 
should  be  considered  together.  This  idea  was  taken 
up  by  other  chemists,  notably  by  Gmelin  in  his  Hand- 
book, and  many  analogies  and  groups  were  sought  for. 
In  1857  Lennsen  returned  to  this  grouping,  endeavor- 
ing to  force  all  the  elements  into  some  twenty  groups. 
Then  Odling  sought  to  build  upon  them  an  elaborate 
system  of  the  elements  which  he  called  the  Natural 
System.  Such  groupings  were  often  forced  and  failures. 


84  HISTORY  OF  CHEMISTRY 

The  science  was  not  far  enough  advanced  to  enable  one 
to  understand  the  real  meaning  of  these  regularities. 

Gladstone's  Ascending  Series.  —  The  first  to  suggest 
an  arrangement  of  the  elements  in  the  order  of  their 
atomic  weights,  beginning  with  hydrogen,  was  Gladstone 
(1853).  These  numbers  were  too  faulty  and  there  was 
too  much  confusion  in  them  to  yield  any  satisfactory 
results,  but  the  principle  was  an  important  one.  Mani- 
festly nothing  in  the  way  of  interrelation  or  regularity 
was  to  be  found  in  tables  alphabetically  arranged.  In 
1863  de  Chancourtois  made  use  of  the  revised  atomic 
weights  in  an  ascending  series  which  he  called  the  tel- 
luric screw.  He  drew  as  a  conclusion  from  his  work 
that  the  properties  of  an  element  are  determined  by 
atomic  weight.  This  was  a  fundamental  proposition  in 
the  Periodic  System  which  was  later  announced  by 
MendeleefL  In  the  work  of  Newlands,  which  followed 
closely  upon  that  of  de  Chancourtois  (the  first  publi- 
cation appearing  in  1864),  there  is  a  nearer  approach 
to  the  Periodic  System.  He  also  arranged  the  elements 
according  to  their  atomic  weights  and  observed  that 
the  eighth  element  was  analogous  to  the  first,  and  so  on 
through  the  list  with  an  interval  of  seven.  This  he 
called  the  law  of  octaves.  There  were  many  difficulties 
and  inconsistencies  so  that  little  support  was  attracted 
to  it.  Meyer's  table,  published  in  the  same  year,  was 
arbitrary  as  to  the  sequence  of  the  elements,  arranged  in 
sixes,  and  was  too  faulty  to  receive  much  attention. 

Periodic  System.  —  It  was  Mendeleeff,  a  Russian 
chemist,  who,  independently  and  with  a  wealth  of  chem- 
ical facts  adduced  in  its  support,  gave  to  the  science  its 
central  system,  bringing  order  out  of  much  confusion. 


NATURE  OF  THE  ATOM  85 

Because  the  elements  fell  in  periods  of  sevens  and  threes 
it  was  named  the  Periodic  System.  The  basic  law  was 
given  in  this  form:  "The  properties  of  the  elements  are 
functions  of  their  atomic  weights."  So  nearly  is  this 
true  that  Mendeleeff  was  able  to  predict  the  existence 
of  certain  elements,  giving  a  number  of  their  properties. 
These  were  later  discovered  and  the  prophecies  con- 
firmed. It  required  an  insight  into  the  principles  of 
this  system  to  devise  the  later  table  given  by  Mendel- 
eeff, and  the  conclusions  reached  by  him  give  evidence 
that  he  had  grasped  these  principles.  The  most  impor- 
tant of  these  were: 

1.  The  elements,  if  arranged  according  to  their  atomic 
weights,  exhibit  an  evident  periodicity  of  properties. 

2.  Elements  which  are  similar  as  regards  their  chem- 
ical  properties   have   atomic  weights  which   are   either 
nearly  of  the  same  value  or  which  increase  regularly. 

3.  The  arrangement  of  the  elements  in  the  order  of 
their  atomic  weights  corresponds  to  their  so-called  val- 
ences as  well  as  to  some  extent  to  their  distinctive  chem- 
ical properties. 

4.  The  elements  which  are  most  widely  diffused  have 
small   atomic   weights. 

5.  The  magnitude  of  the  atomic  weight  determines 
the  character  of  the  element  just  as  the  magnitude  of 
the  molecule  determines  the  character  of  a  compound 
body. 

The  table  of  Mendeleeff  was  changed  but  little  for 
thirty  years.  Its  anomalies,  as  the  omission  of  hydro- 
gen and  the  rejection  of  the  atomic  weight  as  the  decid- 
ing factor  in  such  cases  as  cobalt  and  nickel,  tellurium 
and  iodine,  etc.,  were  recognized;  but  greater  knowl- 


86  HISTORY  OF  CHEMISTRY 

edge  was  needed  before  these  could  be  explained  or  the 
underlying  law  grasped. 

The  Zero  Group.  —  In  discussing  the  Periodic  System 
it  had  been  pointed  out  by  mathematicians  that  the 
transition  per  saltum,  as  from  fluorine  to  sodium  or 
chlorine  to  potassium  (that  is,  an  increase  of  electro- 
negative character  until  the  maximum  was  reached  in 
fluorine  and  then  an  abrupt  change  to  the  highly  elec- 
tro-positive sodium),  could  not  take  place  without  first 
passing  through  either  zero  or  infinity.  When  Ramsay 
announced,  near  the  close  of  the  nineteenth  century,  the 
discovery  of  argon,  helium,  and  the  other  monatomic 
gases  and  it  was  found  that  these  had  no  combining 
power,  no  electro-chemical  character,  and  no  valence 
and  were  the  only  known  monatomic  gases  at  ordinary 
temperature,  it  was  seen  that  the  zero  group  had  been 
found  and  the  table  rounded  off.  The  periods  were  no 
longer  sevens  but  eights,  besides  the  short  periods  of 
three. 

Contributions  from  Radioactivity.  —  The  study  of 
radioactive  phenomena  began  in  the  first  decade  of  the 
twentieth  century.  The  radioactive  elements,  with  every 
proof  of  their  elemental  character,  increased  by  nearly 
fifty  per  cent  the  number  of  known  elements.  How 
could  they  find  places  in  the  system  which  was  already 
a  bit  crowded  and  in  some  confusion  over  the  placing 
of  the  rare  earths?  First,  it  was  found  that  certain  gas- 
eous ones  belonged  to  the  zero  group.  Then  Soddy 
announced  his  theory  of  isotopes,  namely,  that  there 
might  be  several  elements  which  were  so  much  alike 
chemically  that  they  could  not  be  separated  by  chemical 
means  and  yet  differed  in  their  atomic  weights.  Their 


NATURE  OF  THE  ATOM  87 

chemical  properties  were  to  be  taken  as  decisive  and  they 
belonged  in  one  place  in  the  system  in  spite  of  their 
atomic  weights.  Another  contribution  from  radioactiv- 
ity was  a  method  of  deciding  the  location  of  an  element 
by  counting  the  recoil  particles.  A  few  years  later  Mose- 
ley,  by  his  remarkable  work  in  photographing  X-ray 
spectra  discovered  a  method  by  which  this  location 
could  more  easily  and  surely  be  settled.  In  this  way 
were  confirmed  the  exceptions  made  in  the  beginning 
in  placing  cobalt  and  nickel,  etc.  Fortunately  in  most 
cases  the  determining  factor  coincides  with  the  atomic 
weight,  or  influence  of  mass.  Otherwise  the  discovery  of 
the  Periodic  System  would  have  been  long  delayed. 
Composite  Nature  of  the  Atom.  —  The  arguments 
in  behalf  of  the  composite  nature  of  the  elements  may 
well  be  given  here.  When  these  arguments  were  duly 
weighed  they  caused  more  than  a  wavering  in  the  old 
faith  as  to  the  simplicity  of  the  elemental  atom.  The 
revelations  of  radioactivity  have  disclosed  the  internal 
structure  of  these  particles  so  that  they  are  known  as  no 
longer  ultimate.  Many  chemists  in  the  nineteenth  cen- 
tury regarded  the  atom  not  as  something  which  could 
not  be  divided  but  as  something  which  had  not  been 
divided.  A  study  of  the  Periodic  System  brought  the  con- 
viction that  the  elements  were  closely  interrelated  with 
constituents  common  to  them  all.  Remsen  wrote:  "The 
so-called  elements  are  shown  to  be  related  to  one  another 
and  it  seems  impossible  in  the  light  of  these  facts  to  be- 
lieve that  they  are  distinct  forms  of  matter.  It  seems 
much  more  probable  that  they  are  in  turn  composed 
of  subtler  elements."  Gladstone,  in  an  address  before 
the  British  Association,  said,  "The  remarkable  rela- 


88  HISTORY  OF  CHEMISTRY 

tions  between  the  atomic  weights  of  the  elements  and 
many  peculiarities  of  their  grouping  force  upon  us  the 
conviction  that  they  are  not  separate  bodies  created 
without  reference  to  one  another  but  that  they  have 
been  built  up  from  one  another  according  to  some  general 
plan." 

Evidence  as  to  Complexity.  —  The  first  argument  for 
complexity  is  drawn  from  the  manifest  kinship  shown 
by  the  elements  in  the  Periodic  System.  A  second  ar- 
gument lies  in  the  close  analogies  to  be  observed  be- 
tween the  compound  radical  NH4  and  the  alkali  ele- 
ments, the  compound  radical  CN  and  the  halogens, 
etc.  These  resemble  elements  in  every  respect  except 
that  they  can  be  dissociated  and  built  up  at  will.  The 
presumption  is  strong  that  the  same  might  be  done 
for  the  other  elements  if  only  the  suitable  treatment 
were  known.  Again,  it  is  known  that  when  the  va- 
lence of  an  element  is  changed  the  result  is  comparable 
to  the  formation  of  another  element.  The  analogy 
to  the  homologous  series  of  the  hydrocarbons  was  pointed 
out  by  Cooke,  Dumas,  and  others.  Lastly,  the  number  of 
lines  found  in  the  spectra  of  the  elements  can  not  well 
be  referred  to  the  motion  of  absolutely  simple  bodies. 
The  matter  has  been  finally  settled  by  the  phenomena 
of  radioactivity,  which  have  shown  elements  in  the 
process  of  disintegration  and  new  elements  forming  and 
have  justified  the  conclusion  that 'the  atoms  are  made 
up  of  discrete  units  of  positive  and  negative  electricity 
and  are,  therefore,  storehouses  of  enormous  energy. 
So  far,  and  one  may  add  fortunately,  no  means  of  re- 
leasing this  energy  is  at  our  command.  Theories  as 
to  the  structure  of  the  atom  and  the  disposition  of  this 


NATURE  OF  THE  ATOM  89 

energy  have  been  advanced  by  Rutherford,  Bohr,  Lang- 
muir,  and  others.  It  will  be  seen  that  the  Periodic  Sys- 
tem thus  receives  its  explanation  and  the  series  of  ele- 
ments can  be  theoretically  built  up  of  the  two  simplest 
atoms,  hydrogen  and  helium.  This,  however,  is  as  yet 
only  in  a  tentative  stage.  Valence  and  the  electro-chem- 
ical characteristics  also  receive  at  least  a  rational  ex- 
planation, whether  final  or  not,  and  advanced  chemistry 
has  entered  the  sub-atomic  or  ultimate  stage. 


CHAPTER  XI 

AFFINITY,   THE  ATOMIC  ATTRACTIVE  FORCE 

It  was  seen  from  the  very  earliest  times  that  the  hy- 
pothesis of  the  atomic  constitution  of  matter  involved 
also  an  investigation  as  to  the  force  which  brought  about 
the  union  of  atoms  and  held  them  in  combination.  This 
was  a  problem  which  the  earliest  philosophers  found 
themselves  incapable  of  solving  because  of  their  general 
ignorance  as  to  the  natural  forces  and  the  paucity  of 
their  experimental  or  other  data. 

The  oldest  idea  as  to  the  cause  of  the  union  of  two 
substances  was  that  they  must  contain  some  common 
principle.  Thus  Hippocrates  (460-357  B.C.)  taught 
as  one  of  the  fundamental  doctrines  that  "'like  would 
unite  only  with  like."  This  doctrine  gave  rise  to  the 
term  used  at  present,  affinity,  though  this  ancient  belief, 
cherished  for  centuries,  has  long  since  been  lost  sight  of. 

The  term  affinitas  seems  to  have  been  used  first  by 
Albertus  Magnus  to  indicate  the  cause  of  the  union  of 
silver  and  other  metals  with  sulphur.  The  same  ex- 
pression was  used  by  chemists  following  him  and  in 
very  nearly  the  same  sense  as  at  present.  Glauber,  Boyle, 
Hooke,  and  others  found  it  useful  to  designate  the  un- 
known combining  force.  Still  it  was  inferred  that  some 
similarity  must  exist  between  the  combining  substances. 
The  greater  the  affinity,  the  greater  the  resemblance. 
With  the  eighteenth  century  there  came  a  change  in 

90 


AFFINITY,  THE  ATOMIC  ATTRACTIVE  FORCE      91 

this  belief.  Boerhaave  sought  to  show  that  affinity  was 
also  evinced  by  dissimilar  bodies  in  their  tendency  to 
combine.  Solution  was  looked  upon  as  an  act  of  affinity. 
Boerhaave  maintained  that  the  solution  of  iron  in  nitric 
acid  was  also  an  act  of  affinity  and  that  no  relationship 
existed  between  the  two,  but  that  they  were  essentially 
different.  His  influence  as  a  teacher  and  the  wide  dis- 
tribution of  his  text-books  secured  the  introduction  and 
general  adoption  of  his  views  by  chemists.  Yet  physicists 
opposed  the  idea  of  a  new  force.  The  term  attraction 
used  by  Newton  was  too  indefinite  and  general  to  displace 
affinity,  which  by  that  time  had  become  fully  incorporated 
into  chemical  literature,  in  spite  of  the  recognition  that 
the  latter  term  was  based  upon  a  mistaken  idea. 

Strength  of  Affinity.  —  The  knowledge  of  this  force 
grew  very  slowly.  First,  it  was  recognized  that  the 
force  varied  in  strength.  Glauber  maintained  that 
the  tendency  of  one  body  to  unite  with  another  differs 
in  accordance  with  the  nature  of  the  latter  and  that 
another  substance  can  bring  about  the  decomposition 
of  such  a  union  when  it  has  a  greater  affinity  for  one 
of  the  components  than  they  have  for  one  another.  And 
so  it  came  about  that  two  approximate  tests  were  de- 
vised for  measuring  the  strength  of  affinity.  First,  the 
readiness  of  combination  and  secondly,  the  displacement 
of  one  substance  in  combination  with  another.  Obser- 
vations began  to  accumulate.  Glauber  and  Stahl  and 
others  announced  certain  affinity  series.  In  1718  Geof- 
froy  published  sixteen  tables,  called  by  him  tables  des  rap- 
ports, and  then  followed  a  number  of  tables  by  different 
chemists,  the  best  and  most  widely  known  being  the 
tables  of  Bergman  in  1775.  Bergman  recognized  the  fact 


92  HISTORY  OF  CHEMISTRY 

that  chemical  affinity  is  influenced  and  varied  by  tem- 
perature, differing  also  with  the  physical  state  of  the 
substances.  Berthollet  stated  that  it  was  affected  by 
mass.  He  considered  it  as  probably  "a  phase  of  the 
same  fundamental  property  of  matter  as  that  to  which 
universal  gravitation  owes  its  origin."  The  differences 
observable  between  the  two  he  attributed  to  the  prox- 
imity of  the  reacting  substances  in  the  case  of  affinity 
and  to  the  influence  of  special  conditions.  Berzelius 
offered  as  an  explanation  of  affinity  the  hypothesis  that 
it  was  dependent  upon  electrical  attraction.  This  seems 
to  have  been  first  a  conception  of  Davy.  According 
to  the  thinking  of  Berzelius,  each  atom  is  endowed  with 
a  certain  quantity  of  electricity,  partly  positive  and  partly 
negative,  which  accumulates  in  particular  parts  of  the 
atoms  and  gives  to  each  a  positive  and  a  negative  pole. 
The  atom  as  a  whole,  however,  has  the  character  of 
either  a  positively  or  negatively  electrified  body  be- 
cause of  the  preponderance  of  one  or  the  other  kind  of 
electricity.  When  two  atoms  combine  their  respective 
charges  are  neutralized.  Of  course  this  offers  an  ex- 
planation of  the  greater  attraction  between  unlike  atoms. 
Every  molecule  then  was  built  up  of  two  parts,  one 
positively  and  the  other  negatively  charged,  and  thus 
formed  a  dual  structure.  The  theory  was  known  as  the 
dualistic  theory.  In  the  imperfect  knowledge  of  the 
day  difficulties  presented  themselves,  especially  in  the 
matter  of  the  same  element  (as  hydrogen)  sometimes 
substituting  a  positive  element  and  again  a  negative  one, 
and  hence  the  theory  lost  support.  It  is  astonishing  how 
closely  it  approaches  the  modern  theory  as  to  the  con- 
stitution of  the  atom  and  attractive  binding  force. 


AFFINITY,  THE  ATOMIC  ATTRACTIVE  FORCE      93 

Measurement  of  Affinity.  —  Various  attempts  have 
been  made  at  measuring  the  relative  strength  of  affinity, 
but  the  many  conditions  which  influence  chemical  re- 
actions and  the  lack  of  definite  knowledge  as  to  the 
nature  of  the  force  to  be  measured  render  the  question 
a  very  complex  one,  and  no  satisfactory  solution  has  been 
reached.  The  formation  of  a  compound  is  accompanied 
by  changes  of  energy;  also  the  application  of  energy 
can  cause  the  dissociation  of  a  compound.  It  would 
seem  to  be  simple  to  measure  the  energy  liberated  or 
applied,  but  even  then  the  results  would  be  of  little 
value  unless  the  connection  with  affinity  were  accurately 
known.  The  part  played  by  heat  in  reactions  was,  of 
course,  a  matter  of  early  experience.  The  measurement 
of  the  heat  evolved  in  chemical  reactions  has  led  to  the 
development  of  the  branch  of  chemistry  known  as  thermo- 
chemistry. The  first  law  discovered  was  that  of  La- 
voisier and  Laplace,  namely,  that  for  the  dissociation 
of  a  compound  into  its  constituents  the  same  amount  of 
heat  is  absorbed  as  was  evolved  in  its  formation.  This 
is  true  for  endothermic  reactions  also  where  heat  is  ab- 
sorbed on  combination  and  the  same  amount  given  off 
on  dissociation.  In  1840  Hess  announced  the  impor- 
tant principle  that  in  a  chemical  reaction  the  amount  of 
heat  evolved  is  the  same  whether  the  process  takes  place 
step  by  step  or  in  one  step.  This  removed  many  difficul- 
ties which  lay  in  the  way  of  the  determination  of  this 
evolved  heat.  Thermochemistry  was  further  built  up  by 
the  work  of  Favre  and  Silbermann,  and  especially  by 
that  of  Thomsen.  It  is  possible  to  arrive  at  some  knowl- 
edge of  relative  affinities  by  the  study  of  analogous  re- 
actions. Thus  in  the  union  of  hydrogen  with  chlorine, 


94  HISTORY  OF  CHEMISTRY 

bromine,  and  iodine  the  heats  of  formation  are  respect- 
ively 44,000,  16,660,  and  12,072  calories.  These,  how- 
ever, are  not  to  be  taken  as  proportional  to  the  affini- 
ties involved  but  simply  as  varying  in  the  same  order. 
As  Remsen  says,  "The  difficulties  are  much  increased 
in  more  complicated  cases  and  it  will,  therefore,  be  seen 
that  it  is  impossible  to  measure  the  affinity  by  means 
of  the  heat  evolved  in  reactions." 

Again,  it  would  seem  that  there  is  some  connection 
between  this  combining  force  and  the  electrical  states 
of  the  atoms.  Much  stress  has  been  laid  upon  this  but 
little  is  really  understood  concerning  it. 

Valence.  —  Still  another  important  property  of  the 
atom  remains  to  be  considered.  This  is  called  valence 
and  is  closely  connected  with  the  phenomena  of  affinity. 
Where  there  is  no  affinity  between  two  atoms  no  valence 
can  be  exhibited.  Valence  decides  the  number  of  atoms 
which  enter  into  a  molecule.  As  both  atoms  have  a  def- 
inite valence,  necessarily  both  have  to  be  taken  into 
account.  The  question  of  valence  did  not  arise  until 
there  had  been  some  development  of  the  theories  as  to 
affinity.  No  necessity  was  felt  for  it  until  the  number 
of  known  compounds  had  been  greatly  multiplied  and 
the  need  for  their  classification  became  pressing.  Valence 
has  also  been  defined  as  the  saturation  capacity  of  the 
atoms. 

Evolution  of  the  Idea.  —  Probably  the  first  concep- 
tion of  valence  was  in  the  recognition  of  the  so-called 
polyatomic  compounds.  This  term  was  first  used  by 
Berzelius  in  1827,  who  applied  it  to  such  elements  as 
chlorine  or  fluorine  where  he  thought  several  atoms  of 
these  elements  united  with  a  single  atom  of  another  ele- 


AFFINITY,  THE  ATOMIC  ATTRACTIVE  FORCE      95 

ment.  This  use  of  the  term  does  not  seem  to  have  re- 
ceived wide  acceptance.  It  was  applied  to  compounds, 
however,  and  for  certain  of  these  its  use  became  general. 
Thus  Graham  applied  it  to  the  acids  combining  with 
various  proportions  of  the  bases.  These  were  called 
polybasic  acids.  Odling  and  Williamson  extended  the 
idea  to  the  compounds  which,  according  to  the  theory 
prevailing  at  that  time,  were  built  upon  types.  Thus 
both  the  type  theory  of  Laurent  and  the  substitution 
theory  of  Dumas  were  involved  in  the  evolution  of  this 
conception.  The  substitution  of  elements  for  one  an- 
other would  naturally  lead  up  to  the  idea  of  the  relative 
value  of  their  atoms.  This  was  called  by  Liebig  the 
replacement  value.  The  comparison  between  these 
atoms  was  inevitable,  as  they  were  generally  substi- 
tuted for  the  same  element  —  either  hydrogen  or  oxygen. 
The  quantities  of  the  various  elements  thus  substitut- 
ing hydrogen  were  regarded  as  the  equivalents  but  when 
the  confusion  between  equivalents  and  atoms  was  cleared 
up  the  pressing  question  became  as  to  how  many  atoms 
were  involved. 

The  Organo-Metallic  Compounds.  —  The  important 
work  of  Frankland  upon  the  series  of  organic  substances 
containing  metals,  known  as  the  organo-metallic  bodies, 
had  much  to  do  with  the  clearing  up  of  the  confusion 
as  to  the  saturation  capacity  of  the  atoms.  This 
work  showed  that  the  pairing  of  the  radicals  with  the 
elements  was  to  be  explained  on  the  ground  of  some 
characteristic  property  of  the  atoms.  Upon  these  ex- 
periments Frankland  founded  the  valence  theory,  the 
germ  of  which  one  can  detect  in  much  that  had  gone 
before,  especially  in  the  law  of  multiple  proportions; 


96  HISTORY  OF  CHEMISTRY 

but  the  idea  had  not  been  clear,  nor  even  expressed  in 
a  name  except  by  the  vague  term  replacement  value 
introduced  by  Liebig. 

Polybasic  Acids.  —  What  is  known  as  the  doctrine 
of  the  polybasic  acids  contributed  to  the  growth  of  ideas 
upon  the  subject  of  saturation  capacity.  Gay-Lussac, 
Gmelin,  and  others  had  held  the  idea  that  in  the  me- 
tallic oxides  one  atom  of  metal  was  united  with  one  atom 
of  oxygen,  and  that  these  oxides  united  with  one  atom 
(molecule)  of  acid  to  form  neutral  salts.  Graham  showed 
by  his  investigations  upon  the  acids  of  phosphorus  that 
this  view  could  be  held  no  longer.  He  proved  that  in 
the  ortho,  pyro,  and  meta  acids  for  each  "atom"  of 
PzOs  there  were  respectively  three,  two,  and  one  "atom" 
of  "basic  water,"  which  could  be  substituted  by  equiva- 
lent amounts  of  metallic  oxides.  The  saturation  capac- 
ity of  these  acids  was  then  dependent  upon  the  "basic 
water."  Liebig  extended  this  to  many  other  acids  and 
distinguished  between  mono-,  di-,  and  tri-basic  acids. 
This  term  basicity,  along  with  the  ideas  inherent  in  it, 
clung  for  some  time  to  the  theory  of  the  saturation  ca- 
pacity of  the  atoms.  One  sees  in  the  above  citation  from 
the  work  of  Graham  the  confused  use  of  the  term  atom. 

Polyatomicity.  —  The  idea  of  basicity  was  extended 
further  to  the  compound  organic  radicals.  Thus  Wurtz, 
in  describing  the  glycerin  compounds,  wrote  of  glycerin 
as  a  tribasic  alcohol.  Manifestly  there  is  confusion 
here  since  glycerin  may  combine  with  three  acid  radicals 
and  the  term  should  be  triacid  alcohol.  The  term  ato- 
micity was,  therefore,  sometimes  used.  Williamson 
attached  the  idea  of  capacity  for  saturation  or  atomic- 
ity of  the  radical  to  the  number  of  hydrogen  atoms 


AFFINITY,   THE  ATOMIC  ATTRACTIVE  FORCE       97 

capable  of  substitution.  He  called  these  radicals  then 
monatomic,  diatomic,  etc.  Wurtz'  study  of  the  amines 
also  bore  upon  this  point  and  it  is  easy  to  see  how  the 
notion  of  atomicity  was  soon  extended  to  the  various 
compound  radicals  known.  The  last  step  was  in  the 
extension  of  this  idea  of  saturation  to  the  elements  them- 
selves. From  their  combinations  and  substitutions  with 
these  organic  radicals  their  atomicity  was  deduced. 

Deduction  of  Valence  from  Inorganic  Compounds.  — 
When  one  considers  the  formulas  of  the  inorganic  chem- 
ical compounds  even  a  superficial  observer  is  attracted 
by  the  general  symmetry  to  be  observed  in  them.  For 
instance,  the  compounds  of  nitrogen,  phosphorus,  anti- 
mony, and  arsenic  show  a  tendency  on  the  part  of  these 
elements  to  form  compounds  in  which  either  three  or 
five  equivalents  of  other  elements  are  contained.  With- 
out formulating  an  hypothesis  to  account  for  this  agree- 
ment in  the  grouping  of  the  atoms,  it  is  clear  that  such  a 
regularity  exists  and  that  the  affinity  of  the  atoms  of  the 
elements  named  is  always  satisfied  by  the  same  number 
of  atoms.  Frankland  did  not  consider  a  higher  valence 
than  five.  Though  he  mentioned  the  simple  inorganic 
compounds  and  used  them  in  illustration,  he  drew  the 
valence  doctrine  from  his  studies  of  complex  organic 
substances. 

Progress  made.  —  The  ideas  advanced  by  Frankland 
did  not  meet  with  immediate  acceptance.  There  was 
a  somewhat  prolonged  discussion  over  the  constitution 
of  the  polybasic  acids  and  other  compound  groups, 
joined  in  by  Odling,  Williamson,  Gerhardt,  Wurtz,  and 
others,  which  showed  the  necessity  for  a  valence  theory 
and  did  much  to  introduce  it  into  the  science.  By  1858 


98  HISTORY  OF  CHEMISTRY 

the  theory  had  made  rapid  progress.  In  this  year  Ke- 
kule  first  deduced  the  valence  of  carbon  from  its  sim- 
plest compounds,  declaring  it  to  be  quadrivalent  or  capa- 
ble of  combining  with  four  hydrogen  atoms.  Hydrogen 
was  taken  as  the  standard  or  unit  with  a  valence  of  one. 
On  this  basis  an  unvarying  valence  of  four  was  assigned 
to  carbon  throughout  all  the  compounds  of  carbon,  or 
organic  chemistry.  This  had  already  been  recognized 
by  Kolbe  and  Frankland,  if  not  expressly  stated  by 
them.  But  Kekule  rendered  further  and  much  greater 
service  by  examining  into  the  manner  in  which  two  or 
more  of  the  quadrivalent  carbons  were  united  with  one 
another.  The  doctrine  of  atomic  chains,  open  and  closed, 
sprang  from  this  and  the  domination  of  the  structural 
idea  in  chemistry  became  complete. 

Following  the  example  set  in  the  compounds  of  carbon, 
it  was  the  fashion  for  some  decades  afterwards  to  as- 
sign a  single  valence  to  each  element  and  so  construct 
the  formulas  of  the  compounds  as  to  agree  with  this. 
The  difficulties  met  with,  and  the  glaring  inconsisten- 
cies, caused  this  effort  to  be  given  up  and  brought  about 
the  recognition  of  the  fact  that  an  element  might  have 
more  than  one  valence.  Further,  where  the  element 
has  more  than  one  valence  the  change  from  one  to  the 
other  can  be  brought  about  by  the  application  of  energy, 
such  as  heat,  light,  chemical  action,  etc.  It  seems  now 
that  the  explanation  of  the  phenomena  of  valence  is 
to  come  through  the  study  of  radioactivity.  The  modern 
conception  of  valence  is  an  outgrowth  of  the  knowledge 
of  the  electrical  constitution  of  the  atom  and  is  based 
upon  the  existence  of  latent  or  valence  electrons  and 
their  interchange. 


CHAPTER  XII 

GROWTH   OF  INORGANIC   CHEMISTRY 

It  has  been  necessary  to  devote  a  good  deal  of  time 
and  space  to  the  evolution  of  the  fundamental  theories, 
since  growth  in  accurate  knowledge  and  real  progress 
depended  upon  these.  They  form  the  foundation  of  the 
modern  science  and  a  correct  understanding  of  them, 
coming  through  a  study  of  their  development,  is  most 
important.  It  is  well  now  to  turn  to  the  multiplication 
of  chemical  facts  and  enlargement  of  the  field  until 
the  science  of  chemistry  had  to  be  subdivided  into  a 
number  of  branches.  In  the  earlier  half  of  the  nine- 
teenth century  there  was  practically  but  one  field  and 
that  was  inorganic  chemistry  in  which  the  metals  and 
most  of  the  elements  are  to  be  considered.  The  dis- 
covery of  new  elements  is  the  first  thing  to  attract  the 
attention. 

Discovery  of  New  Elements.  —  Among  the  early  dis- 
coverers of  new  elements  was  the  distinguished  German 
chemist,  Klaproth  (1743-1817).  It  was  largely  through 
his  influence  that  the  German  chemists  were  won  over 
to  the  views  of  Lavoisier.  He  devoted  himself  mainly 
to  the  analysis  of  minerals  and  the  improvement  of 
analytical  methods.  He  added  uranium  and  titanium 
to  the  list  of  simple  bodies  and  discovered  zirconia  but 
was  unable  to  separate  the  metal  zirconium.  Proust 
did  accurate  and  valuable  work  in  connection  with  the 

99 


100  HISTORY  OF  CHEMISTRY 

study  of  tin,  copper,  iron,  nickel,  cobalt,  antimony, 
silver,  gold,  and  mercury,  thus  contributing  to  the  ex- 
tension of  chemical  knowledge.  But  the  two  most 
distinguished  discoverers  in  the  first  quarter  of  the 
nineteenth  century  were  Davy  and  Berzelius.  Their  in- 
fluence upon  the  science  has  been  very  great  and  more 
extended  mention  is,  therefore,  accorded  them. 

Humphry  Davy  (177&-1829).  —  The  scientific  train- 
ing of  Davy  was  secured  while  apprenticed  to  a  surgeon 
and  apothecary  at  Penzance.  At  the  age  of  twenty  he 
was  put  in  charge  of  the  laboratory  of  the  Pneumatic 
Institution  at  Bristol,  founded  by  Dr.  Beddoes  for  the 
application  of  gases  to  the  treatment  of  diseases.  Davy's 
surroundings  here  were  most  propitious  for  a  successful 
career  of  scientific  investigation.  His  laboratory  was 
well  furnished  and  was  supported  '6y  the  subscriptions 
of  scientific  men.  His  early  experiments  related  chiefly 
to  nitrogen  monoxide.  He  discovered  its  anaesthetic 
action.  While  in  this  laboratory  he  gave  some  of  his 
time  also  to  experiments  upon  the  decompositions  brought 
about  by  means  of  electricity.  Becoming  professor  of 
chemistry  at  the  Royal  Institution  in  London,  he  devoted 
himself  to  the  decomposition  of  some  of  the  substances 
then  regarded  as  simple  or  elementary,  among  them  the 
alkalis  and  alkaline  earths.  In  this  work  he  made  use 
of  a  very  powerful  voltaic  pile. 

Nicholson  and  Carlisle  had  made  the  observation 
in  1800  that  water  was  decomposed  into  its  constituents 
by  the  discharge  from  the  voltaic  pile.  This  led  to  simi- 
lar experiments  upon  other  substances,  among  them  the 
remarkable  ones  of  Berzelius  and  Hisinger  upon  salt  solu- 
tions, ammonia,  sulphuric  acid,  etc.  Davy  was  among 


GROWTH  OF  INORGANIC  OHEMlSTF&Y          \T)i 

the  first  to  busy  himself  with  this  interesting  and  im- 
portant question,  the  decomposition  of  water.  From 
the  very  first  it  was  noticed  that  acid  and  alkaline  sub- 
stances were  formed  and  it  was  believed  by  some  that 
water  was  changed  into  these  through  the  action  of  elec- 
tricity. By  most  careful  experiments  Davy  showed  the 
error  of  this  view.  He  carried  out  this  electrolysis  in  ves- 
sels of  various  materials  and  showed  that  the  products 
mentioned,  acid  and  alkali,  were  due  to  the  glass  ves- 
sels or  to  matter  dissolved  in  the  water  or  to  the  air 
itself.  If  the  water,  distilled  in  silver,  were  electro- 
lyzed  in  gold  vessels  in  an  atmosphere  of  hydrogen  the 
acid  and  alkali  did  not  appear. 

Davy  further  repeated  and  confirmed  the  work  of 
Berzelius  upon  salt  solutions.  He,  too,  observed  that 
the  electric  current  separated  hydrogen,  metals,  metal- 
lic oxides,  alkalis,  and  earths  at  the  negative  pole  and 
oxygen  and  the  acids  at  the  positive.  He  concluded 
that  the  first-named  substances  have  a  positive  elec- 
trical energy  and  the  latter  a  negative;  and  this  was  the 
beginning  of  the  electro-chemical  theory.  Davy  sought 
to  explain  all  chemical  combination  and  decomposi- 
tion on  this  principle.  According  to  him,  the  heat  noticed 
in  certain  cases  of  combination  was  due  to  and  but  a 
manifestation  of  electricity.  Davy  was  the  first  to  put 
in  a  fixed  form  the  conception  that  electrical  and  chem- 
ical action  may  be  referred  to  the  same  force.  All  the 
later  doctrines  that  chemical  changes  are  the  evidences 
of  electrical  attractions  take  their  rise  from  his  work 
and  views. 

Decomposition  of  the  Alkalis.  —  In  his  first  experi- 
ments upon  potash  and  soda  Davy  used  strong  solu- 


'102  HISTORY  OF  CHEMISTRY 

tions  and  noticed  that  only  hydrogen  and  oxygen  were 
evolved.  He  next  passed  the  current  through  melted 
potash.  A  flame  appeared  at  the  negative  pole  and, 
on  changing  the  direction  of  the  current,  "aeriform 
globules  which  inflamed  in  the  air  rose  through  the  pot- 
ash." When  the  potash  was  placed  upon  a  piece  of 
platinum,  which  was  made  the  negative  pole  of  a  power- 
ful battery,  and  the  positive  pole,  in  the  form  of  a  plat- 
inum wire,  brought  in  contact  with  the  upper  surface 
of  the  potash  the  latter  melted  and  small  globules,  lus- 
trous and  metallic  and  much  like  mercury,  were  noticed 
on  the  negative  platinum.  Some  burst  and  burned; 
others  tarnished  and  became  coated  with  a  white  film. 
Great  was  Davy's  delight  at  his  discovery,  and  one 
can  scarcely  exaggerate  the  impression  made  upon  the 
chemical  world  by  the  decomposition  of  this  supposed 
elementary  body,  and  the  remarkable  new  metal  ob- 
tained from  it.  Its  properties  were  quite  the  opposite 
of  those  which  were  held  to  be  characteristic  of  the  metals. 
It  was  light,  oxidized  immediately  in  the  air,  and  contact 
with  water  brought  about  its  decomposition.  Davy 
also  decomposed  soda  in  a  similar  way,  obtaining  a 
metal  with  analogous  properties.  He  confirmed  his  dis- 
covery by  oxidizing  these  metals  back  into  the  original 
alkalis.  He  learned  how  to  prepare  larger  quantities  and 
to  keep  them  under  naphtha.  He  named  these  metals 
potassium  and  sodium.  These  discoveries  were  made  in 
1807  and  were  followed  next  year  by  the  decomposition 
of  the  alkaline  earths,  lime,  baryta,  and  strontia.  He 
was  convinced  by  his  experiments  that  silica,  alumina, 
zirconia,  and  beryllia  could  also  be  decomposed  by  the 
electric  current  but  failed  to  obtain  any  of  the  supposed 


GROWTH  OF  INORGANIC  CHEMISTRY         103 

elements  existing  in  these  substances.  This  he  attrib- 
uted to  his  current  not  being  powerful  enough.  Davy's 
discoveries  confirmed  the  view,  which  was  already  widely 
held,  that  the  alkalis  and  earths  were  metallic  oxides. 
It  was  not  yet  known  that  some  of  these  were  really 
the  hydroxides. 

Composition  of  Muriatic  Acid.  —  Davy's  next  impor- 
tant services  were  in  connection  with  the  theory  of  acids. 
Berthollet,  by  his  work  upon  hydrogen  sulphide,  hydro- 
chloric acid,  and  hydrocyanic  acid,  had  really  shown 
the  untenable  character  of  Lavoisier's  theory  that  oxy- 
gen was  present  in  all  acids  and  hence  deserving  of  its 
name,  the  acid-maker.  But  Berthollet's  experiments 
were  not  pressed  to  their  legitimate  conclusion  and  the 
theory  of  Lavoisier  still  held  its  place,  though  the  ex- 
istence of  hydrochloric  acid  became  a  serious  stumbling 
block.  Oxygen,  according  to  the  theory,  should  be 
one  of  its  constituents;  yet  no  one  could  detect  its  pres- 
ence. If  this  acid  contained  oxygen,  its  salts  should 
also.  In  1774  Scheele  had  shown  that  by  its  action 
upon  the  black  oxide  of  manganese  a  yellow,  pungent- 
smelling  gas  was  obtained.  Berthollet  showed  that 
a  solution  of  this  gas  in  water  gave  off  oxygen  when 
exposed  to  sunlight,  and  hydrochloric  acid  was  formed 
at  the  same  time.  Therefore,  it  was  called  "  oxidized 
muriatic  acid."  Muriatic  acid  was  regarded  as  composed 
of  oxygen  and  an  unknown  radical.  These  were  not  the 
views  of  Scheele,  who  called  the  gas  "dephlogisticated 
muriatic  acid"  and  regarded  it  as  hydrochloric  acid 
deprived  of  its  phlogiston  or  hydrogen.  In  1809  Gay- 
Lussac  and  Thenard  showed  that  one  volume  of  "  oxi- 
dized' muriatic  acid"  and  one  volume  of  hydrogen  united 


104  HISTORY  OF  CHEMISTRY 

to  form  muriatic  acid.  This  proved  that  it  contained 
hydrogen. 

Davy  next  endeavored  to  find  the  oxygen  which  was 
supposed  to  be  in  this  acid,  but  without  success.  He 
did  show,  however,  that  when  " oxidized  muriatic  acid" 
acted  upon  metals  salt-like  compounds  were  obtained, 
and  that  similar  compounds,  and  at  the  same  time  water, 
were  formed  by  the  action  of  muriatic  acid  upon  me- 
tallic oxides.  Davy  explained  these  results  by  regard- 
ing " oxidized  muriatic  acid"  as  an  element  and  muri- 
atic acid  as  its  compound  with  hydrogen,  but  chemists 
were  slow  to  accept  his  views.  Davy  held  that  this 
element,  to  which  he  gave  the  name  chlorine,  resembled 
oxygen  in  many  respects  and  in  a  limited  sense  was 
also  to  be  regarded  as  an  acidifier  and  supporter  of  com- 
bustion. In  the  ensuing  discussion  with  Gay-Lussac, 
who  endeavored  to  prove  from  the  work  of  Berzelius 
and  Davy  on  ammonium  amalgam  and  from  the  action 
of  potassium  on  ammonia  that  hydrogen  was  an  alka- 
lizing principle,  Davy  uttered  the  following  important 
but  often  over-looked  truth:  "The  substitution  of  anal- 
ogy for  fact  is  the  bane  of  chemical  philosophy;  the 
legitimate  use  of  analogy  is  to  connect  facts  together 
and  to  guide  to  new  experiments." 

Davy's  facts  were  clear  and  convincing  and  in  a  few 
years  chlorine  was  generally  accepted  as  an  element. 
In  1812  and  1813  iodine,  discovered  by  Courtois,  a  French 
soap  maker,  and  investigated  by  Gay-Lussac,  was  added 
to  the  list  of  acidifiers. 

The  New  Theory  of  Acids.  —  These  additional  facts 
necessitated  a  revision  of  the  theory  of  acids.  It  came 
about  that  no  one  element  was  any  longer  regarded  as 


GROWTH  OF  INORGANIC  CHEMISTRY          105 

the  acid-making  principle  but  the  acid  properties  seemed 
to  be  dependent  upon  the  other  element  or  elements 
combined  with  hydrogen.  An  acid  might  contain  oxy- 
gen and  be  an  oxy-acid  or  contain  no  oxygen.  So,  too, 
a  salt  might  contain  oxygen  or,  like  the  chlorides  and 
iodides,  have  none  in  its  composition.  Thus  the  old 
view  that  a  salt  was  a  compound  of  the  oxide  of  a  non- 
metallic  element,  or  acid,  and  of  the  oxide  of  a  metal, 
or  base,  was  overthrown  and  salts  came  to  be  looked 
upon  as  metallic  derivatives  of  acids,  a  metal  replacing 
the  hydrogen.  The  only  element  common  to  all  acids 
was  hydrogen. 

The  Alkalizing  Principle.  —  In  this  connection  it  is 
well  to  take  up  the  discussion  which  arose  as  to  the  con- 
stitution of  the  alkali  metals,  sodium  and  potassium. 
Davy  had  observed  that  these  metals  separated  at  the 
negative  electrode,  while  oxygen  appeared  at  the  pos- 
itive when  the  hydroxide  was  electrolyzed ;  also  that 
they  had  the  power  of  reducing  metallic  oxides.  He 
likewise  showed  that  by  their  combustion  in  oxygen 
the  alkalis  seemed  to  be  regenerated.  Hence,  he  con- 
cluded, these  substances  were  metallic  and  elementary. 
From  his  investigation  of  ammonium  amalgam  a  little 
later  he  concluded  that  this  was  composed  of  mercury 
and  a  hypothetical  metal-like  substance,  ammonium, 
which  broke  up  into  hydrogen  and  ammonia.  The  anal- 
ogy between  this  substance  and  the  alkalis  and  the 
similarities  between  their  amalgams  gave  rise  to  the 
theory  that  these  alkali  metals  also  were  combined 
with  hydrogen,  a  theory  which  Davy  was  more  inclined 
to  accept  because  of  the  combustibility  of  these  metals. 
Gay-Lussac  and  Thenard  had  examined  also  the  action 


106  HISTORY  OF  CHEMISTRY 

of  potassium  upon  ammonia  gas  and  noted  the  liberation 
of  hydrogen  and  the  formation  of  a  green  substance, 
the  amount  of  hydrogen  liberated  being  the  same  as  that 
set  free  by  potassium  from  water.  From  the  green  sub- 
stance they  regenerated  the  original  amount  of  ammonia 
used.  Therefore,  they  said  that  potassium  consisted  of 
potash  and  hydrogen  and  that  this  hydrogen  was  set  free 
by  treatment  with  water  or  with  ammonia.  According 
to  this  theory,  there  was  an  alkalizing  hydrogen. 

Davy  soon  returned  to  his  original  ideas  as  to  these 
alkali  metals  and  gave  as  his  explanation  of  the  experi- 
ments of  Gay-Lussac  and  Thenard  that  the  hydrogen 
came  from  the  decomposition  of  the  ammonia  and  not 
from  the  potassium.  In  the  year  1811  Gay-Lussac 
and  Thenard  came  over  to  Davy's  views,  having  observed 
that  the  body  obtained  by  burning  potassium  was  not 
the  same  as  potash  but  contained  less  oxygen,  and  that  the 
melted  potash  was  not  water-free,  as  Davy. had  imagined. 
Thus  they  gave  up  their  theory  that  hydrogen  was  an 
alkalizing  principle  giving  bases  when  combined  with 
ammonia,  soda,  or  potash  and  similar  substances. 

Berzelius  (1779-1848).  —  It  was  peculiarly  fortunate 
for  chemistry  that  two  such  brilliant  and  accurate  in- 
vestigators as  Davy  and  Berzelius  should  have  appeared 
at  a  time  when  the  framework  erected  by  Lavoisier  needed 
filling  out  and  the  foundations  of  the  science  had  to  be 
broadened  and  deepened.  A  succession  of  mediocre 
and  inaccurate  workmen  coming  just  then  would  have 
more  easily  misled  and  more  seriously  retarded  the 
science  than  at  a  later  period.  Berzelius  ranks  as  one 
of  the  greatest  of  chemists  and  the  chemists  of  to-day 
can  scarcely  overestimate  their  indebtedness  to  him. 


GROWTH  OF  INORGANIC  CHEMISTRY          107 

Berzelius  was  born  in  Sweden  one  year  after  the  birth 
of  Davy.  Poverty  greatly  hampered  both  in  their  younger 
years  and  both  were  forced  to  follow  medicine  and  phar- 
macy as  a  means  of  livelihood  at  first.  Berzelius  became 
professor  of  chemistry  in  Stockholm.  Here  he  lacked 
the  appliances  and  the  leisure  afforded  Davy  by  his 
freedom  from  class  work.  Still,  his  lectures  and  classes 
enabled  Berzelius  to  impress  himself  and  his  views  upon 
the  rising  generation  of  chemists,  and  some  of  the  noted 
chemists  received  training  under  him.  His  career  was 
further  comparable  to  that  of  Davy  in  that  he  held  an 
honored  post,  namely,  that  of  permanent  secretary  to 
the  scientific  society  of  his  native  land  and  was  ennobled 
by  his  king. 

Contributions  of  Berzelius.  —  It  is  difficult  to  give 
a  short  and  at  the  same  time  fair  account  of  the  work 
of  this  great  man,  as  it  covered  nearly  the  entire  field 
of  chemistry  and  hence  was  of  the  most  varied  and  ex- 
tensive character.  Only  brief  reference  can  be  made  to 
some  of  the  more  important  work.  It  is  interesting  to 
note  the  difference  between  the  equipment  with  which 
this  work  was  done  which  compares  but  poorly  with  the 
expensive  appliances  and  large  means  which  were  at  the 
command  of  Davy  and  increases  the  wonder  over  what 
he  accomplished.  Wohler,  his  most  distinguished  pupil, 
has  left  a  description  of  his  first  visit  to  the  laboratory 
of  Berzelius  in  which  so  many  famous  discoveries  had 
been  made. 

"No  water,  no  gas,  no  hoods,  no  oven  were  to  be  seen; 
a  couple  of  plain  tables,  a  blow-pipe,  a  few  shelves  with 
bottles,  a  little  simple  apparatus,  and  a  large  water- 
barrel  whereat  Anna,  the  ancient  cook  of  the  establish- 


108  HISTORY  OF  CHEMISTRY 

ment,  washed  the  laboratory  dishes,  completed  the 
furnishings  of  this  room,  famous  throughout  Europe 
for  the  work  which  had  been  done  in  it.  In  the  kitchen 
which  adjoined  and  where  Anna  cooked  was  a  small 
furnace  and  a  sand-bath  for  heating  purposes." 

At  the  time  of  Davy  and  Berzelius  the  chemist  was 
expected  to  be  something  of  a  mechanic,  able  to  cut 
and  form,  fashion  and  solder,  the  wood,  brass,  and  iron 
into  the  various  shapes  he  needed.  He  must  also  have 
skill  as  a  glass  blower,  for  in  most  cases  he  would  have 
to  depend  upon  his  own  cunning  of  hand  for  the  success 
of  his  experiments. 

Analytical  and  Experimental  Work.  —  Berzelius  in- 
troduced many  improvements  in  the  methods  of  ana- 
lytical chemistry,  devising  new  means  of  separating  and 
determining  the  different  elements.  His  close  attention 
to  details  led  him  to  the  discovery  of  selenium,  ceria, 
thoria,  and  many  new  compounds.  He  was  also  the 
first  to  prepare  the  elements  silicon,  zirconium,  and  a 
purer  tantalum,  and  did  much  towards  enlarging  the 
knowledge  of  the  platinum  metals.  He  made  a  great 
number  of  investigations  to  prove  the  law  of  constancy 
of  proportions  and  also  Dalton's  law  of  multiples.  He 
enriched  mineralogy  by  many  analyses  of  minerals  and 
showed  that  minerals  were  simply  naturally  occurring 
chemical  compounds  which  obeyed  the  ordinary  laws 
of  combination.  He  introduced  a  chemical  system 
for  the  classification  of  minerals  based  upon  this  view 
of  their  nature.  He  extended  the  law  of  multiple  pro- 
portions to  organic  chemistry  and  did  much  to  system- 
atize that  branch  of  chemistry. 

Determination   of   Atomic   Weights.  —  Berzelius,    to- 


GROWTH  OF  INORGANIC  CHEMISTRY          109 

gether  with  the  pupils  in  his  laboratory,  undertook  the 
determination  of  the  atomic  weights.  The  analytical 
work,  of  course,  greatly  excelled  in  accuracy  that  of 
Dalton,  and  in  the  rules  laid  down  for  guidance  in  de- 
ciding the  number  of  the  atoms  in  a  given  compound 
or  molecule  he  showed  a  far  greater  knowledge  of  and 
insight  into  chemical  reactions.  Still  his  rules  were 
in  some  respects  arbitrary  and  unsatisfactory.  By  re- 
calculating the  results  from  his  analytical  data  many 
of  his  determinations  have  been  cited  and  utilized  in 
settling  these  physical  constants  in  the  century  which 
has  elapsed  since  his  time.  It  has  already  been  men- 
tioned that  in  1813  this  far-seeing  man  recognized  in 
part  the  distinction  made  by  Avogadro  between  atoms 
and  molecules.  His  first  fairly  complete  table  of  the 
atomic  weights  was  published  in  1818. 

Introduction  of  Symbols.  —  The  rapid  development 
of  the  science  made  it  necessary  to  have  some  short- 
hand method  of  recording  elements,  compounds,  and 
reactions.  Of  course  a  few  symbols  taken  from  ancient 
mythology,  astrology,  etc.,  had  been  used  by  the  al- 
chemists and  iatro-chemists,  and  there  were  later  spo- 
radic efforts  at  shortening  the  record.  Dalton,  for  in- 
stance, had  attempted  to  introduce  certain  diagramatic 
symbols  but  failed  because  of  their  unpractical  nature. 
Thus,  oxygen  was  a  circle  O ;  hydrogen,  a  circle  enclos- 
ing a  dot,  O ;  and  water  became  O  O .  Carbon  was  a 
solid  black  circle,  •  and  carbon  dioxide,  therefore,  was 
O  •  O.  And  so  the  list  went  on  with  large  circles,  barred 
circles,  radiated  circles,  etc. 

Berzelius  greatly  aided  the  progress  of  chemistry  by 
the  introduction  of  a  rational,  simplified  set  of  symbols, 


110  HISTORY  OF  CHEMISTRY 

the  meaning  of  which  was  caught  at  a  glance.  The 
system  was  practically  the  same  as  that  which  has  been 
in  use  ever  since.  He  proposed  that  the  first  letter  of 
the  Latin  name  of  the  element  should  be  used  to  desig- 
nate it  and  that  this  should  represent  one  atom,  or  equiv- 
alent of  it.  A  compound  was  represented  by  placing 
the  proper  number  of  these  symbols  side  by  side.  Thus 
H  is  hydrogen,  Cl  is  chlorine,  and  HC1  is  hydrogen 
chloride.  He  supposed  the  existence  of  certain  double 
atoms  where  two  atoms  of  an  element  occur  together. 
These  were  indicated  by  a  mark  across  the  symbol; 
thus  HO  was  water,  or,  as  it  is  written  now,  H2O.  For 
convenience  sake  an  atom  of  oxygen  was  often  indi- 
cated by  a  dot,  an  atom  of  sulphur  by  a  mark  at  right 
angles.  Thus  carbon  dioxide  C;  potassium  nitrate,  KN. 
The  Dualistic  Theory.  —  In  matters  of  theory  Ber- 
zelius  exercised  also  a  commanding  influence.  The 
combining  power  of  the  atoms  he  attributed  to  their 
electro-chemical  character,  his  view  of  the  atom  being 
that  it  carried  a  distinct  charge.  The  term  atom  was 
extended  by  him  to  include  what  he  looked  upon  as 
compound  atoms.  These  were  built  up  of  two  parts, 
each  of  which  might  be  a  simple  atom  or  several  atoms 
in  which  each  of  the  two  parts  acted  as  a  single,  sim- 
ple atom.  This  was  the  dual  structure  and  formed  the 
dualistic  system  of  Berzelius.  This  theory  has  already 
been  referred  to  and  is  mentioned  again  because  of  the 
system  of  writing  formulas  of  compounds  which  he 
introduced  and  which  was  in  vogue  for  many  years.  Thus 
barium  sulphate  was  supposed  to  be  made  up  of  barium 
oxide  and  sulphur  trioxide,  the  first  positively  charged 
and  the  latter  negatively  charged.  The  formula  was 


GROWTH  OF  INORGANIC  CHEMISTRY         111 

written  BaO.SO3.  So  also  CaO.CO2,  ZnO.SOg,  etc. 
To  write  such  formulas  correctly  required  a  knowledge 
of  the  valences,  both  of  atoms  and  compound  radicals, 
which  was  lacking  at  that  time. 

Additions  to  the  List  of  Elements.  —  During  the  pe- 
riod covered  by  Berzelius  several  new  elements  were 
discovered  by  his  pupils  and  others.  In  1817  Stromeyer 
discovered  cadmium  and  in  the  same  year  Arfvedson 
announced  the  separation  of  lithium.  In  1828  Wb'hler 
succeeded  in  obtaining  aluminum,  beryllium,  and  yt- 
trium. Some  years  later  Mosander  separated  several  of 
the  metals  contained  in  the  rare  earths,  as  lanthanum, 
erbium,  and  terbium.  Bussy  separated  magnesium  in 
1829;  vanadium  was  added  by  Sefstrom  in  1830.  The 
first  of  the  platinum  metals  was  discovered  by  Wood 
in  1741  and  the  last  of  these,  ruthenium,  was  separated 
more  than  a  century  later  —  in  1845  —  by  Glaus.  No 
further  discoveries  were  made  until  the  spectroscope  was 
brought  into  use.  By  its  aid  in  1860  Bunsen  added  two 
new  elements,  rubidium  and  cesium,  and  more  than  a 
dozen  have  been  found  since.  This  delicate  means  of 
testing  also  revealed  the  fact  that  while  many  of  these 
new  elements  constituted  a  very  small  proportion  of 
the  substances  making  up  the  crust  of  the  earth  they 
were  very  widely  distributed;  and  furthermore,  that  the 
sun  and  other  celestial  bodies  were  composed  of  the 
same  sort  of  matter  as  was  to  be  found  on  our  planet, 
and  so  the  universe  was  one  harmonious  whole  as  to 
composition  and  governed  by  the  same  laws.  The  fact 
that  each  element  has  its  distinctive  spectrum  fur- 
nished a  final  test  as  to  whether  or  not  the  substance 
under  examination  was  really  a  new  element.  Depend- 


112  HISTORY  OF  CHEMISTRY 

ence  upon  chemical  methods  and  tests  alone  caused 
many  mistakes  and  something  like  a  hundred  false  an- 
nouncements have  appeared  in  chemical  literature. 

The  Monatomic  Gases.  —  Great  interest  was  aroused 
when  Ramsay  and  Rayleigh  discovered  argon  in  1894, 
and  also  a  few  years  later  when  Ramsay  announced 
the  existence  of  its  companion  gases,  helium,  neon, 
krypton,  and  xenon,  all  of  which  are  found  in  the  at- 
mosphere. The  story  of  the  discovery  illustrates  well 
the  value  of  careful  and  accurate  work  without  neglect- 
ing apparently  trivial  details  and  the  following  up  of 
each  clue  until,  so  far  as  possible,  everything  is  known 
and  understood  about  the  subject  under  investigation. 
It  is  sometimes  stated  that  discoveries  and  important 
advances  are  often  brought  about  through  accident. 
Thoroughness  does  not  admit  of  accident.  It  would 
seem  more  fitting  to  reserve  the  term  for  the  one  who 
had  his  chance  and  missed  it.  The  opportunity  passes 
and  may  never  return.  There  have  been  many  such  un- 
happy instances  in  science. 

In  his  analytical  examination  of  air  in  1785  Caven- 
dish subjected  an  enclosed  volume  to  the  action  of  the 
electric  spark.  Oxygen  was  added  from  time  to  time 
until  there  was  more  than  enough  to  combine  with  all 
of  the  nitrogen.  The  products  and  the  excess  of  oxygen 
were  removed  by  solvents.  It  is  a  testimony  to  the  ac- 
curacy both  of  his  observation  and  reporting  of  details 
that  he  recorded  the  presence  of  a  residue  or  bubble, 
equal  to  about  T^$  of  the  original  volume.  Many  others 
made  use  of  this  method  and  either  failed  to  note  or  to 
report  the  residue,  and  no  attention  was  paid  to  the 
observation  of  Cavendish. 


GROWTH  OF  INORGANIC  CHEMISTRY          113 

More  than  a  century  later  (1894),  while  determining 
the  density  of  nitrogen,  Lord  Rayleigh  found  that  there 
was  a  difference  between  the  density  of  that  prepared 
from  the  compounds  of  nitrogen  and  the  nitrogen  ob- 
tained from  air,  the  latter  being  half  a  per  cent  heavier. 
This  brought  to  mind  the  forgotten  observation  of  Caven- 
dish and  led  to  an  examination  of  air  to  see  whether  it 
contained  any  unknown  gas.  The  investigation  was 
carried  on  jointly  by  Rayleigh  and  Ramsay,  who  pursued 
different  methods  for  removing  the  nitrogen  from  the 
air,  and  their  results  agreed.  The  air  contained  a  gas 
which  would  not  combine  with  anything  else  and  to 
this  new  element  the  name  argon  was  given.  It  forms 
about  one  per  cent  by  volume  of  the  atmosphere  and 
can  therefore  be  prepared  from  it  in  large  quantities. 
It  has  no  combining  power  and  its  molecule  consists  of 
a  single  atom.  It  has  its  distinctive  spectrum  and  can  be 
detected  by  this  means. 

In  the  following  year  Ramsay  examined  a  strange 
gas  which  had  been  reported  as  present  in  certain  ura- 
nium minerals,  thinking  that  this  also  might  prove  to  be 
argon.  He  found  the  spectrum  to  be  quite  different 
and  identified  it  with  the  spectrum  of  one  of  the  ele- 
ments found  in  the  sun  some  thirty  years  earlier  by 
Lockyer  and  named  by  him  helium.  In  the  uranium  min- 
erals the  helium  occurs  along  with  small  amounts  of 
nitrogen  and  argon.  It  is  known  now  to  occur  in  the 
atmosphere,  in  well  and  spring  waters,  and  in  the  natural 
gas  which  is  drawn  from  the  earth  in  many  places.  This 
also  is  a  monatomic  gas  and  forms  no  compounds.  Hy- 
drogen and  helium  are  the  lightest  gases  known  and,  next 
to  hydrogen,  helium  has  the  lowest  atomic  weight  and  is 


114  HISTORY  OF  CHEMISTRY 

the  most  difficult  of  the  gases  to  liquefy.  These  facts 
have  their  bearing  on  the  latest  theory  of  the  composi- 
tion of  the  atoms. 

Many  other  minerals  were  examined  by  Ramsay,  but 
no  further  new  gases  were  obtained  from  them.  A  more 
exhaustive  study  was  then  made  of  the  air,  in  which 
Travers  assisted  Ramsay.  The  method  was  to  take  very 
large  quantities  of  liquid  air  and  examine  the  fractions 
which  evaporated  at  different  temperatures.  In  this 
way,  in  1898,  they  succeeded  in  separating  three  new 
elements  to  which  the  names  neon,  krypton,  and  xenon 
were  given.  These  resembled  helium  and  argon  and 
belonged  to  the  monatomic  group.  Later  Moore  made 
a  still  more  thorough  examination,  evaporating  one  hun- 
dred tons  of  liquid  air,  but  found  no  additional  new 
gases. 

Further  Development  of  Inorganic  Chemistry.  — Dur- 
ing the  century  which  has  elapsed  since  Berzelius  be- 
gan his  most  important  work  a  great  many  able  chem- 
ists have  labored  in  the  field  of  inorganic  chemistry; 
multitudes  of  new  compounds  have  been  formed  and 
studied  and  a  better  understanding  reached  as  to  the 
laws  governing  their  formation  and  decomposition. 
It  is  in  this  way  that  science  grows  —  an  army  of  toil- 
ers in  the  ranks,  a  good  and  competent  captain  here  and 
there,  and,  when  the  emergency  arises,  a  great  strat- 
egist who  leads  the  way  to  masterful  accomplishment 
—  a  Newton,  a  Lavoisier,  a  Dalton,  a  Berzelius,  a  Fara- 
day, a  Mendeleeff.  History  cannot  tell  'the  story  of 
all,  but  each  faithful  private  in  the  ranks  deserves  his 
meed  of  gratitude. 


CHAPTER  XIII 

DEVELOPMENT   OF  ORGANIC   CHEMISTRY 

In  the  text-book  of  Le*mery,  in  use  in  the  latter  half 
of  the  seventeenth  century,  all  chemical  substances 
were  classified  and  separately  treated  under  the  three 
headings,  mineral,  vegetable,  and  animal  substances. 
This  division  seems  to  have  been  made  first  at  this  time 
and  was  the  usual  one  during  the  next  century.  This 
corresponded  with  the  favorite  grouping  of  the  "three 
natural  kingdoms"  which  was  so  much  used  in  books 
on  general  science  a  few  generations  ago.  It  was  the 
animate  and  inanimate  creation,  and  between  the  two 
lay  the  barrier  of  life  or  vital  force  which  was  not  to  be 
transcended.  So  chemists  chiefly  busied  themselves 
with  the  mineral  world,  its  compounds  and  elements 
and  the  wonderful  laws  governing  them,  and  through 
their  study  reached  down  to  the  unchanging  atoms 
upon  which  they  founded  their  faith  and  their  working. 
A  building  on  any  other  foundation  was  as  futile  as  a 
building  on  the  sand. 

The  Views  of  Lavoisier.  —  Here  also  the  master  mind 
came  to  the  rescue.  Beginning  with  the  foundation  of 
stones,  Lavoisier  showed  that  all  of  these  products  of  life 
processes  were  composed  mainly  of  carbon,  hydrogen,  and 
oxygen.  Some  included  nitrogen  and  still  fewer  contained 
phosphorus  and  sulphur.  Before  this  there  was  great 
doubt  and  discussion  as  to  their  composition,  but  Lavoisier 

115 


116  HISTORY  OF  CHEMISTRY 

showed  how  they  could  be  analyzed  with  fair  accuracy. 
Quite  so,  one  might  say  and  many  did  say,  you  can 
tear  down  and  find  of  what  the  building  was  made  but 
you  can  never  rebuild.  Only  this  strange,  evasive,  un- 
knowable vital  force  can  do  that.  Had  man  halted,  blind 
and  impotent,  before  that  man-erected  barrier  he  would 
have  been  without  most  of  the  comforts  of  modern  life, 
and  it  is  doubtful  whether  the  huge  population  now 
inhabiting  the  earth  could  exist.  Chemistry  is  not  merely 
analytical  but  creative,  and  so  chemists  began  to  regard  it. 
Lavoisier  devised  a  system  of  quantitative  analysis  for 
these  substances  so  as  to  decide  their  composition  fully. 
Acid  substances  were  recognized  among  them  and  La- 
voisier accounted  for  their  nature  by  supposing  that  in 
these  cases  the  oxygen  was  combined  with  a  compound 
radical  or  organic  residue.  This  idea  was  later  developed 
by  Berzelius  and  his  followers  until  organic  chemistry 
became  the  chemistry  of  the  compound  radicals.  But 
the  first  tearing  down  of  barriers  came  when  that  erected 
between  the  " vegetable  and  animal  kingdoms"  was 
overthrown  through  the  investigation  of  the  fats  by 
Chevreul.  These  fatty  substances  are  found  in  both 
plants  and  animals  and  Chevreul  proved  that  many  of 
them  were  identical.  He  also  showed  that  the  same  was 
true  of  certain  acids  and  other  substances.  So  the  first 
part  of  the  distinction  was  no  longer  tenable,  but  the  line 
was  still  very  sharply  drawn  between  mineral  substances 
and  the  products  of  plant  and  animal  life.  These  latter, 
it  was  believed,  could  not  be  artificially  formed  out  of 
the  elements  that  composed  them.  They  were  produced 
by  some  mysterious  force,  life,  whose  operations  could 
not  be  imitated.  The  ordinary  laws  governing  chemical 


DEVELOPMENT  OF  ORGANIC  CHEMISTRY       117 

affinity  could  not  be  expected  to  apply  in  this  field  and 
chemical  theories  could  not  explain  the  phenomena 
of  life. 

Views  of  Berzelius.  —  In  1811  Berzelius  attempted 
to  prove  that  organic  substances  were  nothing  more  than 
ordinary  chemical  compounds,  obeying  the  laws  of  con- 
stant and  multiple  proportions  and  offering  a  fair  field 
for  the  application  of  the  atomic  and  other  theories. 
With  improved  appliances  and  analytical  methods  he 
succeeded  in  showing  the  correctness  of  his  views,  but 
only  after  years  of  labor.  In  the  third  decade  of  the  cen- 
tury he  came  to  look  upon  organic  substances  as  composed 
in  the  same  way  as  the  inorganic  compounds  but  having 
compound  radicals  in  the  place  of  elements.  With  a 
satisfactory  definition  of  compound  radical  this  is  the 
basis  of  organic  chemistry,  though  much  work  had  to 
be  done  before  it  was  made  clear.  Berzelius  attempted 
to  apply  his  dualistic  theory  to  the  compound  radicals 
which  were  recognized  by  him.  He  was  in  a  measure 
led  to  take  up  this  idea  of  the  compound  radical  by  the 
research  of  Gay-Lussac  upon  cyanogen,  in  which  he 
showed  that  this  radical  behaved  like  an  element.  At- 
tempts were  multiplied  to  discover  the  various  organic 
substances  which  had  complex  groupings  of  atoms  and 
functioned  as  elements.  Thus  Gay-Lussac  looked  upon 
alcohol  as  ethylen  and  water.  Dobereiner  regarded  oxalic 
acid  as  carbonic  acid  and  carbon  monoxide.  Berzelius 
pointed  out  that  this  was  in  contradiction  to  the  electro- 
chemical theory.  There  was  danger  of  confusion  and  error. 

Isomerism.  —  The  search  for  the  proximate  constit- 
uents in  organic  compounds  brought  about  a  rapid 
development  of  the  science.  There  were  many  efforts 


118  HISTORY  OF  CHEMISTRY 

at  settling  the  chemical  constitution  of  these  substances. 
One  of  the  important  discoveries  made  was  that  of  isom- 
erism.  This  was  at  first  looked  upon  as  an  error,  so 
little  were  chemists  prepared  to  believe  that  substances 
similarly  composed  could  be  chemically  and  physi- 
cally different.  It  was  in  the  year  1823  that  Liebig  an- 
nounced that  his  analysis  of  silver  fulminate  yielded  the 
same  results  as  Wohler  had  obtained  in  the  preceding 
year  for  his  silver  cyanate.  He  was  confident  that  his 
figures  were  correct  and  believed  that  Wohler  must  have 
made  a  mistake.  A  careful  repetition  of  the  analyses 
showed  him  that  both  were  correct.  Thus  it  was  proved 
that  two  substances,  totally  unlike,  could  and  did  have 
the  same  composition.  Gay-Lussac  saw  that  the  only 
explanation  of  this  lay  in  the  different  mode  in  which  the 
elements  were  united  with  one  another.  Berzelius  hesi- 
tated to  accept  the  facts  or  any  generalization  from  them. 
Then  followed  in  1825  Faraday's  discovery  of  an  isomer 
of  ethylen  chloride,  and  in  1827  Wohler's  transformation 
of  ammonium  cyanate  into  urea.  Berzelius  himself  showed 
the  isomerism  existing  between  tartaric  and  racemic 
acids,  and  chemists  became  accustomed  to  the  new  fact 
of  isomerism  for  the  explanation  of  which  the  atomic 
theory  is  so  necessary.  Berzelius  suggested  the  name 
isomerism.  He  also  adopted  as  the  most  plausible  ex- 
planation of  isomerism  the  different  arrangement  of  the 
atoms.  He  seems  to  have  thought  it  a  possibility  to 
determine  the  mutual  relations  of  the  atoms  in  their 
compounds,  or  the  manner  in  which  the  atoms  were  united 
to  the  compound  radicals  or  proximate  constituents. 

The   Synthesis  of    Urea.  —  Many  of    the  naturally 
occurring  minerals  had  been  reproduced  or  synthesized 


DEVELOPMENT  OF  ORGANIC  CHEMISTRY      119 

by  the  chemist,  but  it  was  still  a  common  belief  that 
the  synthesis  or  imitation  of  organic  substances  was 
beyond  the  reach  of  experimental  methods,  as  they  were 
the  products  of  life  itself  and  could  be  formed  only  in 
the  plant  or  animal  tissue.  It  is  true  that  new  organic 
preparations  had  been  made  by  distilling  or  otherwise 
treating  various  products  of  plant  life  but  the  original 
source  or  starting  point  remained  the  same  life  products. 
Chevreul  had  shown  that  the  natural  fats  were  com- 
pounds of  certain  acids  and  the  glycerin  discovered  by 
Scheele,  but  no  one  had  built  up  these  two  components. 

It  was  Wohler's  brilliant  synthesis  of  urea  which 
finally  broke  down  this  barrier,  proving  the  forerunner 
of  many  syntheses  and  inciting  numbers  of  chemists  to 
engage  in  such  interesting  and  valuable  work.  It  was 
in  1828  that  he  undertook  to  prepare  ammonium  cyanate 
by  evaporating  a  solution  containing  ammonium  sul- 
phate and  potassium  cyanate.  The  evaporation  yielded 
crystals  of  urea  instead.  The  same  change  will  take 
place  if  a  solution  of  ammonium  cyanate  alone  is  evapo- 
rated. This  contains  the  same  elements  and  the  same 
number  of  atoms  as  are  present  in  urea.  Heating  the 
solution  brings  about  a  rearrangement  "of  the  elements. 
Thus  NH4CNO  becomes  (NH2)2CO.  The  cyanates  were 
supposed  to  belong  to  the  inorganic  compounds  and  could 
be  prepared  from  the  elements.  Hence  the  synthesis 
was'^complete  without  the  intervention  of  a  hypothetical 
vital  force.  Urea  is  one  of  the  most  interesting  and  best 
known  of  animal  products,  being  the  compound  in  which 
most  of  the  waste  nitrogen  is  eliminated  by  animals, 
and  no  more  striking  example  of  the  fallacy  of  the  old 
assumption  could  have  been  chosen.  While  the  dying 


120  HISTORY  OF  CHEMISTRY 

away  of  the  old  belief  was  not  immediate,  Wohler's 
discovery  is  commonly  pointed  to  as  marking  the  begin- 
ning of  organic  chemistry  as  a  distinct  branch  of  the 
science. 

Organic  Analysis.  —  One  obstacle  to  the  rapid  de- 
velopment of  this  branch  of  chemistry  lay  in  the  imper- 
fection of  the  analytical  methods.  Lavoisier  had  laid 
the  foundations  for  the  correct  analysis  of  organic  sub- 
stances and  Gay-Lussac,  Berzelius,  and  Dobereiner  had 
successively  improved  the  processes.  However,  the  oper- 
ations were  still  slow,  difficult,  and  not  very  accurate. 
In  1830  Liebig  greatly  improved  the  methods  of  analysis 
and  his  processes  have  not  needed  very  many  nor  great 
modifications  to  fit  them  to  the  needs  of  the  present  day. 
Of  course,  as  the  years  passed  gas  and  electricity  sup- 
planted the  charcoal  which  he  used  for  heating.  Im- 
proved methods  for  determining  the  halogens,  nitrogen, 
vapor  densities,  etc.,  were  introduced  by  Carius,  Hofmann, 
Victor  Meyer,  and  others,  so  that  extremely  accurate 
work  can  now  be  done. 

Classification  of  Organic  Substances.  —  A  true  and 
helpful  classification  of  these  substances,  the  known 
number  of  which  was  increasing  so  rapidly,  was  lacking. 
In  1811  Gay-Lussac  and  Thenard,  interpreting  the  results 
of  their  analyses,  had  divided  them  into  three  classes: 

1.  Those  which  contain  just  so  much  oxygen  as  is 
necessary   to   form  water  with   the   hydrogen   present. 
These  were  carbohydrates. 

2.  Those  containing  less  than  that  porportion  of  oxygen. 
These  were  the  resins  and  oils. 

3.  Those  containing  more  oxygen.     These  were  con- 
sidered the  acids. 


DEVELOPMENT  OF  ORGANIC  CHEMISTRY       121 

Of  course,  so  primitive  and  faulty  a  classification  as 
this  was  of  little  service.  For  instance,  it  quite  ignored 
the  many  hydrocarbons  which  contain  only  carbon  and 
hydrogen.  It  merely  serves  to  show  that  in  the  formative 
stage  of  the  conceptions  held  as  to  these  substances  no 
satisfactory  classification  was  possible. 

Extension  of  the  Electro-Chemical  Theory.  —  In  1819 
Berzelius  declared  that  his  electro-chemical  theory  could 
not  be  extended  to  organic  chemistry,  as  here  these 
elements  were  under  the  influence  of  life  force.  In  decay, 
fermentation,  etc.,  he  saw  evidences  of  a  striving  on  the 
part  of  these  elements  to  return  to  their  normal  con- 
dition. He  later  extended  both  this  theory  and  that  of 
dualism  to  this  branch  of  chemistry,  seeing  in  the  com- 
pound radicals  the  same  dualistic  condition  which  he 
thought  existed  in  what  he  called  the  compound  atoms  of 
inorganic  substances. 

Extension  of  the  Radical  Theory.  —  There  was  con- 
tinued effort  at  extending  the  radical  theory  to  organic 
chemistry.  Thus  in  1828  Dumas  announced  that  ethylen 
was  such  a  radical  and  gave  a  table  of  its  compounds, 
endeavoring  to  show  their  analogy  to  ammonia  and  its 
compounds: 

Olefiant  gas  or  ethylen,  20^2 ;  NH3,  ammonia. 

Hydrochloric  acid  ether,  2C2H2.HC1;  NH3.HC1,  ammonium 
chloride. 

Ether,  4C2H2.H2O;  2NH3.2H2O,  ammonium  oxide. 

Alcohol,  4C2H2.2H2O. 

Acetic  ether,  ^^.CgHeOa.HaO;  2NH3 . CsHeOs . H2O,  am- 
monium acetate. 

Oxalic  ether,  4C2H2.C4O8.H2O;  2NH3 . C4O8 . H2O,  ammonium 
oxalate. 


122  HISTORY  OF  CHEMISTRY 

It  was  a  part  of  this  theory  that  the  radicals  could  be 
separated  and  were  capable  of  independent  existence. 
This  was  called  the  Aetherin  theory  and  was  largely 
based  on  the  ease  with  which  alcohol  could  be  converted 
into  ether  and  ethylen.  In  this  the  aetherin  C4H4  was 
a  base,  forming  hydrates  with  water  and  salt-like  ethers 
with  acids.  This  must  serve  as  an  illustration  of  the  im- 
perfect attempts  at  discovering  these  radicals  and  the 
great  difficulties  attending  such  researches. 

The  Benzole  Acid  Radical.  —  The  radical  theory 
received  its  greatest  support  from  the  classical  research 
of  Liebig  and  Wohler  in  1832  On  the  Radical  of  Benzoic 
Add.  This  was  hailed  by  Berzelius  as  heralding  the 
dawn  of  a  new  day.  It  was  at  least  an  epoch-making 
contribution,  standing  out  as  a  masterpiece  amid  much 
that  was  erroneous  and  misleading  in  the  work  of  the  day. 
These  two  great  chemists,  then  young  men,  showed  that 
in  the  oil  of  bitter  almonds  (benzaldehyde)  and  its  many 
derivatives  one  group  of  atoms  remained  unchanged 
and  characterized  the  whole.  This  they  called  benzoyl 
and  assigned  to  it  the  formula  Ci4HioO2,  or  the  present 
formula  doubled.  Benzaldehyde  itself  was  this  radical 
with  hydrogen,  CwHioC^+Ek;  the  radical  plus  oxygen 
was  benzoic  acid;  with  chlorine  it  was  benzoyl  chloride, 
etc. 

Changes  in  the  Radical  Theory.  —  This  brilliant  re- 
search aided  greatly  in  the  advancement  of  organic  chem- 
istry by  the  valuable  new  methods  of  research  which  it 
introduced  into  the  practice  of  the  chemist.  Furthermore, 
a  new  principle  was  recognized.  Hitherto  it  had  been 
thought  necessary  to  isolate  the  radical,  and  it  was  the 
great  difficulty  or  even  impossibility  of  doing  this  that 


DEVELOPMENT  OF  ORGANIC  CHEMISTRY      123 

rendered  much  of  the  work  futile.  Benzoyl  had  not 
been  isolated  and  was  not  known  except  in  compounds, 
but  one  could  as  little  afford  to  doubt  its  existence, 
since  its  compounds  were  known,  as  to  question  the  ex- 
istence of  magnesium  or  aluminum,  whose  compounds 
were  well  known  a  long  time  before  the  metals  them- 
selves were  separated.  Thus  chemists  were  aroused  to 
search  for  the  common  radicals  in  substances  which 
showed  by  their  chemical  behavior  or  modes  of  prepara- 
tion that  they  should  be  grouped  together. 

Berzelius  and  Liebig  entered  upon  this  work  with 
much  success.  The  difficulty  in  recognizing  benzoyl  as 
a  radical  because  of  its  containing  oxygen  was  done  away 
with  by  regarding  it  as  the  oxide  of  the  real  radical.  The 
early  idea  of  a  radical  was  that  it  was  a  compound  of  car- 
bon and  hydrogen  only  and  contained  no  oxygen.  Thus 
ether  was  the  oxide  of  the  radical  ethyl,  but  Berzelius 
missed  the  connection  with  alcohol  by  regarding  that 
as  the  oxide  of  the  radical  C2H6.  This  was  corrected 
by  Liebig,  who,  however,  doubled  the  formula  of  the 
radical  ethyl  C2H5.  So  for  him  alcohol  was  the  hydrate 
of  ethyl  C4H10O.H20. 

Chemists  agreed  as  to  the  existence  of  compound  radi- 
cals in  these  various  compounds.  It  is  not  surprising 
that  they  should  differ  as  to  the  nature  of  the  radicals 
themselves  when  one  considers  that  this  was  really  only 
the  beginning  of  organic  chemistry  and  the  knowledge  of 
these  substances  was  very  imperfect.  Berzelius  was  in- 
clined to  the  belief  that  these  radicals  were  unchangeable. 
Liebig  took  a  wider  view  of  them,  looking  upon  his  group- 
ing of  the  elements  merely  as  a  means  to  a  better  under- 
standing of  the  transformations  these  bodies  undergo. 


124  HISTORY  OF  CHEMISTRY 

But  despite  minor  differences,  the  brilliant  chemists  who 
have  been  cited  had  obtained  an  insight  into  the  basic 
principles  of  classification  for  organic  substances.  The 
hydrocarbons  do  function  here  as  the  elements  and  do 
form  compounds  which  correspond  to  the  hydroxides, 
oxides,  halides,  sulphides,  etc.  But  since  they  themselves 
are  capable  of  combination  and  change  there  is  a  be- 
wildering versatility  and  great  multiplication  and  com- 
plexity of  the  compounds  formed. 

Compound  Radicals.  —  About  1837  this  theory  of  the 
compound  radicals  reached  its  highest  point  of  credit  and 
influence,  and  organic  chemistry  became  the  chemistry 
of  the  compound  radicals.  Liebig  and  Dumas  united  in 
valuable  investigations,  and  a  citation  from  a  joint  pub- 
lication of  theirs  will  serve  to  show  how  far  they  carried 
the  classification: 

"  Organic  chemistry  possesses  its  own  elements,  play- 
ing at  one  time  the  role  of  chlorine  or  oxygen,  at 
another  that  of  a  metal.  Cyan,  benzol,  amide,  the 
radicals  of  ammonia,  of  the  fats,  of  alcohol,  form  the 
true  elements  of  organic  nature;  whilst  the  simplest  con- 
stituents, as  carbon,  hydrogen,  oxygen,  and  nitrogen 
become  recognizable  only  when  the  organic  material 
has  been  destroyed." 

A  year  later  Liebig  clearly  defined  a  compound  radical, 
giving  three  essential  characteristics  and  using  cyanogen 
as  a  type: 

1.  We  call  cyan  a  radical  because  it  is  an  unchanging 
constituent  in  a  series  of  substances  or  compounds. 

2.  Because  it  can  be  substituted  in  these  by  other 
simple  bodies. 

3.  Because   in   its   compounds   with   a   simple  body 


DEVELOPMENT  OF  ORGANIC  CHEMISTRY       125 

this  last  can  be  separated  and  substituted  by  another 
simple  body. 

At  least  two  of  these  conditions  must  be  fulfilled  for 
a  group  of  atoms  to  be  regarded  as  a  radical. 

This  radical  theory  aroused  great  interest  and  stimu- 
lated chemists  to  much  fruitful  and  even  brilliant  work. 
Special  mention  may  be  made  of  the  research  of  Bunsen 
upon  the  kakodyl  compounds  which  formed,  indeed,  one 
of  the  strongest  supports  of  the  theory. 


CHAPTER  XIV 

FURTHER  THEORIES  AS  TO   STRUCTURE 

Atomic  Theory  Confirmed.  —  The  dualistic  theory 
and  that  of  the  compound  radicals  were  necessarily 
founded  upon  the  atomic  theory  of  Dalton.  As  they 
were  discussed  and  struggled  over  and  became  intrenched 
in  the  science  they  rendered  the  atomic  theory  an  indis- 
pensable assumption.  Even  when  dualism  became  dis- 
credited and  organic  chemistry  took  on  a  different  sig- 
nificance from  that  of  the  chemistry  of  the  compound 
radicals  atoms  were  still  necessary,  and  the  only  possible 
changes  were  in  the  conceptions  of  the  nature  of  the  ulti- 
mate particles. 

Substitution  Theory  and  Overthrow  of  Dualism. — 
Doubts  began  to  arise  as  to  the  theory  of  dualism.  Du- 
mas and  other  chemists  felt  that  Berzelius  had  pressed 
his  theory  too  far.  It  was,  however,  the  discovery  of  the 
principle  of  substitution  which  really  dealt  this  theory  its 
deathblow  and  paved  the  way  for  the  so-called  unitary- 
theory.  Substitution  might  have  been  deduced  from  the 
old  idea  of  equivalence.  It  was  also  touched  upon  in  the 
researches  of  Mitscherlich  upon  isomorphism,  Other 
facts  led  up  very  nearly  to  it.  But,  as  so  often  happens, 
the  thought  and  its  suggestion  were  brought  about  through 
an  accident. 

Substitution  of  Chlorine  for  Hydrogen.  —  In  1834  Du- 
mas was  called  upon  to  examine  into  the  cause  of  certain 

126 


FURTHER  THEORIES  AS  TO  STRUCTURE       127 

irritating  vapors  coming  from  wax  candles  used  to  illu- 
minate the  Tuileries.  He  found  that  in  bleaching  the  wax 
chlorine  had  been  used  and  some  of  the  chlorine  remaining 
in  the  candles  had  caused  the  disagreeable  fumes.  These 
consisted  of  hydrogen  chloride,  the  hydrogen  coming 
from  the  wax.  Dumas  felt  that  this  could  not  be  ex- 
plained on  the  ground  of  a  mechanical  retention  of  the 
chlorine  as  an  impurity.  He  then  fully  investigated  the 
action  of  chlorine  upon,  wax  and  kindred  organic  sub- 
stances. He  found  as  a  result  of  his  investigations  that 
hydrogen  in  organic  compounds  may  be  exchanged  for 
chlorine,  volume  for  volume.  Wohler  and  Liebig  had 
shown  in  1832  that  in  preparing  benzoyl  chloride  out  of 
oil  of  bitter  almonds  by  the  action  of  chlorine  two  atoms 
of  chlorine  took  the  place  of  two  atoms  of  hydrogen. 
This  was  contrary  to  the  central  idea  of  dualism,  since 
chlorine  was  electro-negative  and  should  never  substitute 
electro-positive  hydrogen.  Additional  facts  accumulated. 
Liebig  had  shown  that  by  the  action  of  bleaching  powder 
and  chlorine  upon  alcohol  chloroform  and  chloral  were 
formed.  He  misunderstood  the  constitution  of  these 
compounds  but  Dumas  determined  correctly  their  con- 
stitution and  their  relation  to  alcohol,  showing  here  the 
far-going  substitution  of  chlorine  for  hydrogen. 

Trichloracetic  Acid.  —  Dumas  by  his  substitution  of 
chlorine  for  hydrogen  in  acetic  acid,  forming  trichloracetic 
acid,  secured  the  most  important  support  for  his  theory 
of  substitution.  It  can  be  seen  from  what  he  wrote  re- 
garding this  acid  what  his  views  were  as  to  substitution, 
and  how  the  discovery  of  the  acid  supported  them.  In 
trichloracetic  acid  there  are  three  of  the  hydrogen  atoms 
of  acetic  acid  substituted  by  chlorine. 


128  HISTORY  OF  CHEMISTRY 

"It  is  a  chlorinated  vinegar,"  says  Dumas,  "but  it 
is  remarkable,  and  the  more  so  for  those  who  dislike  to 
find  in  chlorine  a  body  capable  of  substituting  hydrogen 
in  the  exact  and  full  sense  of  the  word,  that  this  chlorinated 
vinegar  is  still  an  acid  like  ordinary  vinegar.  Its  acid 
power  has  not  been  changed.  It  neutralizes  the  same 
amount  of  base  as  before.  It  possesses  the  same  acidity 
and  its  salts,  compared  with  the  acetates,  show  an  agree- 
ment full  of  interest." 

Thus  it  was  shown  that  the  views  of  dualistic  structure 
were  too  rigid  and  a  hindrance  to  the  development  of 
organic  chemistry.  A  negative  atom  could  be  substituted 
for  a  positive  and  the  compound  radical  began  to  be  re- 
garded as  an  atomic  structure  in  which  one  atom  could 
be  substituted  for  another  without  regard  to  its  electro- 
chemical nature.  Laurent  showed  that  Dumas'  state- 
ment as  to  substitution  did  not  hold  good  for  all  cases. 
Often  more  chlorine  was  taken  up,  and  sometimes  less 
than  corresponded  to  thev  volume  of  hydrogen  lost.  As 
the  substituted  body  showed  certain  analogies  to  the 
original,  he  maintained  that  the  chlorine  took  the  place 
held  by  the  hydrogen  in  the  molecule  and,  to  a  certain 
extent,  played  the  same  role. 

Unitary  Theory.  —  The  views  as  to  substitution  met 
with  vigorous  opposition  and  had  to  be  modified  in  some 
particulars,  but  soon  the  molecule  came  to  be  regarded 
as^a  unitary  and  not  a  dualistic  structure.  Thus  there 
were  two  opposing  theories:  The  older,  dualistic,  looked 
upon  the  molecules  as  double  natured  and  composite 
yet  forming  one  unchangeable  whole  in  which  the  members 
lost  their  individuality  and  the  nature  of  these  molecules 
was  determined  by  the  quality  of  the  atoms;  the  new, 


FURTHER  THEORIES  AS  TO  STRUCTURE       129' 

unitary,  theory  maintained  that  the  number  of  the  atoms 
and  their  arrangement  determined  in  the  main  the  nature 
of  the  compound,  and  that  this  molecule  was  not  un- 
changeable but  that  the  atoms  comprising  it  could  be 
substituted  by  others  without  a  complete  change  of  nature. 

Nucleus  Theory.  —  Laurent  was  led  to  propound 
further  the  nucleus  theory  which  was  largely  adopted. 
This  was  in  some  respects  an  elaboration  of  the  compound 
radicals.  Many  of  the  ideas  in  this  theory  have  been 
incorporated  in  the  science,  though  the  theory  itself 
has  been  dropped.  This  theory  sprang  from  the  old  radical 
theory  but  with  an  important  difference,  i.e.,  the  radical 
here  is  not  an  unchanging  group  of  atoms  but  a  com- 
bination which  can  be  changed  through  the  substitution 
of  equivalents.  It  is  but  a  step  in  the  evolution  of  the 
modern  theory,  as  seen  in  the  benzene  nucleus. 

Type  Theory.  —  The  idea  of  types  was  introduced 
by  Laurent  and  Gerhardt  and  was  applied  to  both  in- 
organic and  organic  chemistry.  It  was  rapidly  taken 
up  and  became  the  dominant  structural  theory  of  chem- 
istry in  the  fifth  decade  of  the  nineteenth  century.  Ac- 
cording to  this  theory,  potassium  hydroxide  was  conceived 
to  be  not  a  compound  of  the  oxide  and  water  but  rather 
a  derivative  of  water  in  which  one  atom  of  hydrogen 
was  substituted  by  potassium.  This  was  called  the  water 
type.  Gerhardt  recognized  three  types  —  water,  hydro- 
chloric acid,  and  ammonia  —  and  endeavored  to  classify 
all  compounds  under  one  or  the  other  of  these  types. 
Gradually  it  was  seen  that  other  types  were  needed 
and  the  derivation  from  types  became  more  and  more 
complicated. 

Berzelius,  now  an  old  man,  contended  for  his  dual- 


130  HISTORY  OF  CHEMISTRY 

istic  theory  and  could  not  be  reconciled  to  the  change 
to  the  types  and  to  the  unitary  theory.  But  the  great 
master  was  engaged  in  a  vain  struggle.  In  the  course 
of  the  discussion  he  formulated  a  new  theory  as  giving 
a  better  explanation  of  the  substitution  phenomena  and 
as  being  more  in  consonance  with  his  dualistic  theory. 
This  was  known  as  the  theory  of  conjugated  compounds 
and  associated  with  it  was  the  theory  of  copulas.  The 
ideas,  however,  were  not  very  clear  and  exerted  little  in- 
fluence upon  the  science. 

The  discovery  of  the  amines  in  1848,  the  year  after  the 
death  of  Berzelius,  did  much  to  strengthen  the  type 
theory.  This  was  followed  shortly  by  the  important 
work  of  Williamson  on  the  ethers,  alcohols,  esters,  and 
acids,  which  he  showed  belonged  to  the  water  type. 
It  should  be  noted  that  these  types  were  drawn  from  in- 
organic compounds,  thus  building  upon  that  which  was 
already  fairly  well  known.  The  two  great  divisions  of 
chemistry  have  proved  mutually  helpful  in  their  de- 
velopment al^d  must  always  be  regarded  as  parts  of  one 
harmonious  whole.  Throughout,  the  question  of  chemical 
constitution  has  been  the  important  one. 

Homologous  Series.  —  This  was  a  period  of  classifica- 
tion—  one  of  striving  after  a  systematic  arrangement 
of  the  elements  in  inorganic  chemistry  and  the  radicals 
in  organic.  Pettenkofer,  hoping  for  an  all-embracing 
system,  compared  the  elements  with  the  compound  radi- 
cals and  suggested  that  they  might  be  looked  at  from  the 
same  standpoint.  The  analogies  between  the  radicals 
themselves  had  been  noted  and  Schiel  suggested  that 
they  might  be  arranged  in  series  which  would  bring  out 
this  homology.  The  suggestion  was  adopted  by  Dumas 


FURTHER  THEORIES  AS  TO  STRUCTURE       131 

with  regard  to  the  fatty  acids  and  the  idea  was  further 
extended  by  Gerhardt.  Dumas  transferred  the  idea  to 
inorganic  chemistry  and  tried  to  arrange  the  elements  in 
homologous  series,  but  the  analogies  were  too  incomplete 
for  success.  As  the  knowledge  of  the  organic  radicals 
grew  and  the  fullness  of  their  agreement  was  recognized, 
homologous  series  became  a  necessary  fixture  in  organic 
chemistry. 

Application  of  the  Valence  Theory.  —  It  was  at  this  time 
that  the  valence  theory  took  its  rise  from  the  study  of 
the  organo-metallic  bodies.  With  its  introduction  struc- 
tural organic  chemistry  had  a  secure  foundation.  Its 
founder  was  Kekule*,  who  was  born  about  a  year  after 
Wohler's  noted  synthesis  of  urea.  In  1858,  while  pro- 
fessor at  Ghent,  he  showed  by  a  study  of  the  simpler 
compounds  of  carbon  that  its  valence  was  four.  Later 
he  became  professor  at  Bonn,  dying  there  in  1896. 

Taking  his  arrangement  of  the  halogen  compounds  of 
methane,  it  will  be  seen  how  he  applied  valence  to  the 
type  theory  of  which  he  was  a  strong  supporter.  The 
series  runs:  CH4,  CH3C1,  CH2C12,  CHC13,  CC14.  The 
quadrivalence  of  carbon  remains,  while  the  valence  of  the 
radicals  CH3,  CH2,  etc.,  increases  by  one  with  each  hydro- 
gen lost.  But  his  most  original  idea  was  in  regard  to  com- 
pound radicals  containing  more  than  one  carbon  atom. 
His  conclusion  here  was  that  the  carbon  atoms  were 
directly  connected  with  each  other.  Thus  the  ethyl  radi- 
cal would  be  CH3-CH3;  the  propyl  CH3-CH2-CH3, 
the  hydrogens  being  joined  to  the  carbons  and  the  latter 
forming  an  open  chain.  Kekule's  desire  in  constructing 
these  formulas  was  not  merely  to  show  how  the  atoms 
were  united  but  to  give  a  picture  of  the  way  in  which  re- 


132  HISTORY  OF  CHEMISTRY 

actions  took  place.  So  these  formulas  were  called 
rational.  He  regarded  as  the  most  rational  the  one 
which  at  the  same  time  expressed  the  greatest  number 
of  metamorphoses. 

The  writing  of  the  first  graphic  formulas  was  attempted 
by  Couper,  also  in  1858.  He  insisted,  however,  upon 
halving  the  atomic  weight  of  oxygen  and  this  necessitated 
writing  two  atoms  of  oxygen  where  modern  formulas 
would  show  only  one.  This  was  a  disadvantage  in  the 
matter  of  making  a  favorable  impression  and  receiving 
recognition.  In  1861  Kekule  published  the  first  volume 
of  his  epoch-making  text-book  which  presented  fully  to 
the  public  his  views  upon  structural  organic  chemistry, 
illustrated  by  a  very  large  number  of  examples.  Kekule 
also  gave  as  his  explanation  of  the  differences  between 
the  two  great  divisions  of  organic  substances  the  open 
chain  and  closed  chain  formulas,  thus  satisfactorily  clear- 
ing up  many  difficulties  and  paving  the  way  for  the  re- 
markable development  of  organic  chemistry  which  fol- 
lowed in  the  next  decades.  These  two  divisions  were 
called,  respectively,  the  fatty  (later  aliphatic)  and  the 
aromatic  (cyclic)  series.  In  the  former  methane  and  its 
homologues  were  the  dominant  radicals;  in  the  latter, 
benzene. 

The  Benzene  Theory. —  The  so-called  aromatic  group 
or  series  of  substances  showed  usually  a  higher  ratio  of 
carbon  to  hydrogen  than  did  the  aliphatic.  Where  the 
ratio  was  the  same  or  approximately  the  same  the  stabil- 
ity and  capacity  to  form  compounds  were  much  greater 
in  the  aromatic  group.  Thus  dipropargyl  and  benzene 
both  have  the  formula  CeHe,  but  the  former  is  quite 
unstable  while  the  latter  stands  the  action  of  the  strongest 


FURTHER  THEORIES  AS  TO  STRUCTURE       133 

acids.  Manifestly  the  difference  could  only  be  accounted 
for  by  assuming  a  different  arrangement  of  the  atoms. 
But  to  find  an  arrangement  which  would  account  for 
such  unusual  stability  was  a  perplexing  problem.  It  is 
best  to  give  in  Kekule's  own  words  the  account  of  how 
he  reached  a  solution,  bearing  in  mind  that  the  case 
cited  above  was  not  the  only  one;  nor  was  it  the  special 
one  with  which  he  was  concerned. 

"I  was  busy  writing  on  my  text-book  but  could  make  no 
progress  —  my  mind  was  on  other  things.  I  turned  my 
chair  to  the  fire  and  sank  into  a  doze.  Again  the  atoms 
were  before  my  eyes.  Little  groups  kept  modestly  in  the 
background.  My  mind's  eye,  trained  by  the  observation 
of  similar  forms,  could  now  distinguish  more  complex 
structures  of  various  kinds.  Long  chains  here  and  there 
more  firmly  joined;  all  winding  and  turning  with  a  snake- 
like  motion.  Suddenly  one  of  the  serpents  caught  its 
own  tail  and  the  ring  thus  formed  whirled  exasperat- 
ingly  before  my  eyes.  I  woke  as  by  lightning  and  spent 
the  rest  of  the  night  working  out  the  logical  consequences 
of  the  hypothesis.  If  we  learn  to  dream  we  shall  perhaps 
discover  truth.  But  let  us  beware  of  publishing  our 
dreams  until  they  have  been  tested  by  the  waking 
consciousness." 

This  was  the  origin  of  the  benzene  ring,  an  assumption 
which  expanded  through  the  labors  of  many  workers 
into  the  accepted  theory  of  the  present  and  the  basis 
of  many  of  the  most  remarkable  and  important  achieve- 
ments of  creative  chemistry. 

Stereochemistry.  —  One  manifest  lack  in  these  struc- 
tural formulas,  if  they  were  intended  to  give  a  complete 
picture  of  the  molecule,  is  that  they  are  written  on  plane 


134  HISTORY  OF  CHEMISTRY 

surfaces  and  hence  confined  to  space  of  two  dimensions, 
whereas  they  must  of  necessity  occupy  space  of  three  di- 
mensions. A  perspective  representation  is  also  necessary. 
It  was  Van't  HofE  who,  in  1874,  while  still  a  student,  fas- 
tened attention  upon  this  and  laid  down  the  governing 
principles  a  little  later  in  his  book  Chemistry  of  Space. 
This  branch  of  chemistry  is  known  as  stereochemistry. 
Necessarily  perplexities  and  difficulties  increase  if 
chemists  are  restricted  to  a  knowledge  of  chemical 
reactions  as  the  sole  means  of  determining  these  space 
relations.  An  observation  made  by  Laue  in  1913,  his 
subsequent  work,  and  that  of  the  Braggs,  father  and  son, 
have  introduced  a  new  method,  at  least  for  crystalline 
structure,  in  the  X-ray  spectra.  And  already  much 
progress  has  been  made  both  for  organic  and  inorganic 
molecules  and  the  outlook  is  most  promising  for  further 
revelations.  By  this  method  the  molecules  are  actually 
photographed  and  can  be  studied  in  all  the  accuracy  of 
detail  and  perspective.  Success  turns  on  the  correctness 
of  interpretation  of  the  results. 

Pasteur  (1822-1895).  —  One  of  the  greatest  of  scien- 
tific men,  as  well  as  one  of  the  greatest  benefactors  of 
his  race,  was  Louis  Pasteur.  Born  of  a  peasant  family 
in  a  small  French  village  he  revolutionized  the  science 
of  medicine  when  he  introduced  and  proved  his  germ 
theory  of  disease.  He  also  accomplished  much  for  the 
wine  and  other  industries  of  his  native  land. 

His  most  important  contributions  to  chemistry  came 
through  his  investigation  of  the  tartaric  acids  and  in 
general  the  phenomena  of  physical  isomerism.  There 
are  four  of  these  acids  having  the  same  formula.  Their 
separate  existence  can  not  be  accounted  for  by  the  usual 


FURTHER  THEORIES  AS  TO  STRUCTURE       135 

method  of  possible  changes  in  the  arrangement  of  the 
atoms,  yet  they  do  exist  and  exhibit  certain  physical  dif- 
ferences. One  of  these  extra  forms  had  been  known 
for  a  long  time  as  racemic  acid.  It  is  often  found  in  grapes 
along  with  tartaric  acid  and  sometimes  has  substituted 
to  a  considerable  extent  the  normal  tartaric  acid  in  the 
juice.  Its  acid  potassium  salt  is  more  soluble  than  that 
of  tartaric  acid  and  hence  does  not  separate  out  well 
in  the  aging  of  wine  and  renders  the  wine  of  inferior  quality. 
Pasteur  noticed  that  the  sodium  ammonium  salt  de- 
posited two  kinds  of  crystals.  These  crystals  showed 
hemihedral  faces  so  related  that  one  crystal  corresponded 
to  the  image  in  the  mirror  of  the  other.  He  found  further 
that  the  acid  from  one  variety  of  crystals  was  dextro- 
rotary  while  that  from  the  other  was  laevo-rotary. 
This  is  referable  immediately  to  space  arrangement, 
as  was  represented  in  the  mirror  image.  As  he  published 
an  account  of  his  work  in  1848,  it  marks  the  beginning 
from  which  stereochemistry  was  later  developed.  Pre- 
vious observers,  notably  Biot,  had  remarked  a  connection 
between  optical  rotation  and  hemihedral  forms  in  such 
crystals  as  quartz,  and  it  had  been  shown  that  the  geo- 
metrical form  determined  the  direction  of  the  rotation. 
When  one  recalls  that  Pasteur's  observations  were  made 
with  solutions  in  the  tube  of  the  polariscope  and  also 
that  later  it  was  found  that  this  property  was  also  ex- 
hibited in  the  gases  of  certain  volatile  organic  substances 
it  becomes  possible  to  trace  the  phenomenon  directly 
back  to  the  molecule.  The  construction  of  the  molecule 
also  evidently  determined  the  crystal  form.  Considering 
such  facts  as  these,  Pasteur  reached  the  conclusion  that 
the  molecule  itself  was  unsymmetrical.  It  is  now  known 


136  HISTORY  OF  CHEMISTRY 

that  tartaric  acid  contains  two  unsymmetrically  arranged 
carbon  atoms.  In  the  undeveloped  state  of  organic  chem- 
istry at  that  time  Pasteur  was  unable  to  refer  the  lack 
of  symmetry  to  any  definite  atoms. 

His  study  of  fermentations  and  brilliant  work  in  trac- 
ing these  changes  to  the  life  processes  of  micro-organisms 
have  transformed  the  outlook  of  more  sciences  than  one 
and  wrought  miracles  for  human  comfort,  health,  and 
happiness.  His  name  will  be  associated  always  with 
the  conquering  and  control  of  contagious  diseases. 

Syntheses  from  Coal  Tar.  —  The  foundations  for  the 
important  coal  tar  industries,  especially  relating  to  dye 
stuffs,  were  laid  by  Hofmann  (1818-1892)  and  the  first 
artificial  or  synthetic  color  was  made  in  1856  by  Perkin, 
one  of  his  students.  Hofmann  was  at  that  time  a  pro- 
fessor in  the  Royal  College  of  Chemistry  in  London. 
At  the  time  of  his  death  he  was  a  professor  in  the  Univer- 
sity of  Berlin. 

Tar  is  recovered  as  a  by-product  in  the  distillation  of 
coal  and  until  the  middle  of  the  nineteenth  century  little 
use  had  been  found  for  it  beyond  its  use  as  fuel.  In  1843 
Hofmann  found  that  it  contained  aniline  and  this  led 
to  his  valuable  researches  upon  the  amines.  In  1845 
he  found  that  it  also  contained  benzene  and  the  synthetic 
production  of  aniline  in  large  quantities  from  this  source 
followed.  In  1856,  in  the  course  of  his  investigation  of 
the  action  of  oxidizing  agents  upon  crude  aniline  oil, 
Perkin  discovered  the  dye  known  as  mauve.  This  was 
the  first  of  the  coal  tar  colors.  Griess,  another  assistant 
of  Hofmann,  studied  the'diazo  compounds  and  the  manu- 
facture of  the  azo  compounds  and  dyes  was  founded 
upon  the  results  of  his  researches.  In  1868  Graebe  and 


FURTHER  THEORIES  AS  TO  STRUCTURE       137 

Liebermann  prepared  alizarin,  the  red  coloring  matter 
of  madder,  from  anthracene.  After  some  years  of  costly 
and  toilsome  work  at  a  later  period  Baeyer,  who  had 
studied  under  Bunsen  and  was  then  a  professor  at  Munich, 
worked  out  the  synthesis  of  indigo  from  naphthalene. 
These  discoveries  mark  the  triumphant  progress  of  a 
great  industry  which  soon  branched  out  from  the  arti- 
ficial reproduction  of  natural  coloring  matters  into  an 
almost  unlimited  field  of  creation  of  brilliant  colors  un- 
known before.  Here  the  constitution  of  the  molecules 
was  painstakingly  worked  out  and  the  chromophoric 
groups  of  atoms  identified. 

Further,  plant  perfumes  were  synthesized  and  new  ones 
prepared.  So,  too,  with  the  remedial  agents.  New 
organic  preparations  were  studied  as  to  their  physiological 
properties  and  action  and  the  field  of  synthetic  medicines 
opened  up.  This  required  cooperation  between  the  chemist 
and  the  physiologist  and  many  skilled  workers  entered 
this  field.  New  and  terrible  explosives  were  discovered 
and  then  others  sought  for  among  these  organic  com- 
pounds; and  in  these  later  years  the  deadly  poison  gases 
were  manufactured  for  use  in  warfare.  For  good  or  ill, 
chemistry  as  a  creative  art  came  into  its  own.  The 
modern  world  has  become  dependent  upon  chemical  re- 
search and  the  knowledge  and  skill  of  the  technical 
chemist. 


CHAPTER  XV 
PHYSICAL  CHEMISTRY 

While  in  one  sense  physics  and  chemistry  are  distinct 
branches  of  science,  both  are  concerned  with  the  same 
great  natural  laws.  The  atom  and  the  electron  belong 
to  both  and  now  that  matter  in  its  ultimate  analysis 
has  been  identified  with  energy  there  is  scarcely  a  dividing 
line  between  them.  In  the  earlier  stages  of  their  develop- 
ment one  might  be  both  physicist  and  chemist  and  often 
was.  The  great  accumulation  of  facts  and  theories  has 
rendered  it  practically  impossible  to  be  master  in  both. 
Where  the  two  sciences  merge  into  one  another,  however, 
a  new  branch  has  grown  up  and  this  is  called  physical 
chemistry.  Its  growth  has  been  rapid  and  its  importance, 
both  in  pure  and  applied  science,  can  scarcely  be  over- 
estimated. 

Physical  chemistry  may  be  said  to  have  had  its  beginning 
in  the  teachings  of  Berthollet  in  his  Essai  de  statique 
chimique  published  in  1801.  He  brought  to  light  the  fact 
that  a  chemical  reaction  depended  upon  the  masses,  or, 
as  it  would  be  expressed  now,  the  concentration  of  the 
reacting  substances;  and  that  solubility,  volatility,  and 
such  physical  properties  of  the  products  influence  materi- 
ally the  course  of  the  reactions.  Under  certain  conditions 
equilibria  were  reached.  The  importance  of  these  ob- 
servations was  not  realized  at  that  early  date.  Chemists 
were  busied  with  what  they  regarded  as  more  important 

138 


PHYSICAL  CHEMISTRY  139 

work  —  the  discovery  and  accumulation  of  facts  and  the 
testing  of  the  more  obvious  fundamental  laws. 

Such  investigators  as  Gay-Lussac  with  his  gas  laws, 
Avogadro  and  Ampere  with  their  basis  of  the  kinetic 
theory,  Dulong  and  Regnault  with  their  researches  upon 
specific  heat  and  the  laws  controlling  its  action,  were  most 
prominent  among  the  early  builders  in  this  middle  ground 
between  the  sciences.  A  still  greater  influence  was  exerted 
by  Bunsen  some  fifty  years  later.  In  cooperation  with 
Kirchoff  he  constructed  the  spectroscope  which  has  con- 
tributed so  much  to  the  knowledge  of  nature  and  its 
changes  both  on  the  earth  and  in  the  extra-terrestrial 
bodies.  By  means  of  this  instrument  Kirchoff  showed 
that  radiations  are  absorbed  by  the  vapors  of  the  sub- 
stances which  emit  them,  and  so  revealed  the  meaning 
of  the  dark  lines  which  had  been  found  in  the  solar  spectra. 
Other  absorption  spectra  are  given  by  solutions  the  exact 
physical  explanation  of  which  is  still  an  unsolved  problem. 
Bunsen's  photochemical  investigations  taught  that  the 
degree  of  change  brought  about  by  light  was  proportional 
to  the  intensity  of  the  light  and  the  time  of  exposure, 
and  that  the  light  absorbed  in  a  reacting  medium 
was  proportional  to  the  change  produced.  His  "  photo- 
chemical induction"  is  yet  without  satisfactory  expla- 
nation. Still  it  was  of  first  importance  to  learn  that 
photochemical  absorption  followed  the  usual  laws.  The 
invention  of  the  polariscope  and  the  study  of  polarization 
phenomena,  the  progress  of  hydrolysis,  etc.,  aided  greatly 
in  the  development  of  physical  chemistry. 

Law  of  Mass  Action.  —  As  has  been  pointed  out,  the 
basis  for  this  was  laid  by  Berthollet,  but  its  bearing 
was  not  realized  and  the  observations  were  practically 


140  HISTORY  OF  CHEMISTRY 

forgotten.  After  half  a  century  had  elapsed  the  details 
were  gradually  worked  out.  Thus  Wilhelmy,  in  his  in- 
vestigations upon  the  inversion  of  sugars  by  acids,  studied 
the  hydrolysis  of  sugars  by  means  of  acids  under  con- 
ditions in  which  temperature,  acids,  etc.,  were  varied. 
From  these  observations  he  deduced  a  mathematical  ex- 
pression for  the  velocity  of  the  reaction.  A  little  later 
Berthelot  examined  the  hydrolysis  of  the  esters.  Guldberg 
and  Waage,  after  more  extended  investigation,  summarized 
the  results  and  proposed  as  a  law  which  would  cover  the 
known  facts  that  when  an  equilibrium  has  been  reached 
the  velocity  of  a  reaction  is  determined  by  the  product 
of  the  active  amounts  of  the  interacting  substances. 
To  account  for  the  relationships  obtaining  in  hetero- 
geneous equilibria  the  phase  rule  has  been  adopted. 
The  essential  principles  involved  in  this  were  worked  out 
by  Willard  Gibbs,  whose  work  was  published  in  1876. 
This  rule  is  now  a  matter  of  everyday  application  in  work 
which  would  otherwise  prove  very  baffling. 

Electrolytic  Dissociation.  —  With  the  announcement  by 
Arrhenius  in  1887  of  his  theory  of  electrolytic  dissociation 
the  importance  of  physical  chemistry  and  its  intimate 
bearing  upon  the  ordinary  reactions  and  phenomena  of 
the  laboratory  began  to  be  recognized  and  the  attention 
of  chemists  generally  was  attracted  to  it.  Much  work  had 
been  done  previously  on  electrolytic  association  but  at 
various  times  and  in  a  disconnected  way.  Arrhenius 
gathered  these  facts  in  addition  to  his  own  observations, 
showing  the  connection  between  them  and  the  important 
conclusions  to  which  they  led.  Faraday  had  found  that 
in  the  decomposition  of  an  electrolyte  by  an  electric 
current  definite  amounts  of  the  products  are  obtained  at 


PHYSICAL  CHEMISTRY  141 

the  electrodes  on  the  expenditure  of  a  given  quantity 
of  electricity  and  these  amounts  are  in  equivalent  weight 
proportions.  The  intensity  of  the  current  necessary  for 
the  dissociation  was  determined,  in  his  opinion,  by  the 
strength  of  the  attraction  holding  the  molecules  together. 
He  concluded  that  the  atoms  or  radicals  composing  the 
electrolyte  acted  as  the  carriers  of  the  current  and  called 
them  ions,  naming  the  positive  electrode  anode  and  the 
negative  cathode,  and  the  ions  anions  and  cations,  re- 
spectively. At  first  the  assumption  was  that  the  anion 
and  the  cation  migrated  with  equal  velocities.  Hittorf 
showed  that  this  was  not  the  case.  Williamson  introduced 
the  idea  that  a  molecule  was  not  a  rigid  structure  always 
made  up  of  the  same  identical  atoms  but  was  capable 
of  exchanging  with  corresponding  atoms  of  neighboring 
molecules.  Thus  an  ion  did  not  pass  directly  from  one 
electrode  to  the  other  but  migrated  from  one  molecule 
to  the  next,  effecting  the  necessary  interchange.  Clausius 
adopted  this  idea  of  exchange  and  brought  additional 
facts  to  its  support.  Later  Kohlrausch  carried  out  many 
experiments  upon  the  conductivity  of  solutions  and  con- 
firmed the  work  of  Hittorf.  His  conclusion  was  that  each 
ion,  regardless  of  the  electrolyte  of  which  it  was  a  com- 
ponent, had  a  definite  migration  velocity  which  might 
be  measured  by  its  relation  to  some  standard. 

Physical  Properties  of  Solutions.  —  The  problem  of 
what  takes  place  in  solutions  was  next  attacked  from  a 
different  point  of  view.  It  had  been  known  for  a  long  time 
that  the  freezing  point  of  a  liquid  is  lowered  by  dissolving 
various  substances  in  it;  also  the  vapor  pressure  is  lowered 
or,  as  ordinarily  expressed,  the  boiling  point  is  raised  when 
the  liquid  contains  substances  in  solution.  No  regularity 


142  HISTORY  OF  CHEMISTRY 

had  been  observed,  however,  nor  law  deduced.  The  only 
observation  bearing  on  this  is  that  of  Blayden,  who  worked 
in  the  laboratory  of  Cavendish.  He  studied  the  influence 
of  various  dissolved  substances  upon  the  lowering  of  the 
freezing  point  and  found  that  when  he  compared  solutions 
of  the  same  compound  the  degree  of  lowering  was  pro- 
portional to  the  amount  of  substance  dissolved. 

In  1881  Raoult  took  up  the  investigation  of  this  lowering 
of  the  freezing  point  and  showed  by  his  experiments  that 
when  different  substances  were  used  with  the  same  sol- 
vent the  lowering  of  the  freezing  point  in  each  solution 
was  inversely  proportional  to  the  molecular  weight  of 
the  substance  dissolved.  Hence  if  the  quantities  taken 
were  proportional  to  the  molecular  weights  the  degree  of 
lowering  would  be  the  same.  Turning  then  to  the  in- 
fluence of  such  dissolved  substances  upon  the  boiling  point 
he  found  an  analogous  influence  upon  the  raising  of  the 
boiling  point.  In  the  hands  of  other  investigators  it  was 
soon  found  that  the  matter  was  not  so  easily  solved. 
There  were  many  irregularities  and  exceptions  which 
demanded  explanation.  The  statement  that  behavior 
in  solutions  was  independent  of  the  nature  of  the  solvent 
and  of  the  dissolved  substances  could  not  be  generally 
applied  and  was  not  true  in  that  form,  j  The  difficulties 
were  removed  and  the  explanation  made  clear  by  experi- 
ments carried  out  along  an  apparently  different  line. 

Osmotic  Pressure.  —  More  than  one  hundred  years 
earlier  Nollet  had  observed  that  when  water  and  alcohol 
are  separated  by  a  membrane  the  water  passes  through 
the  membrane  into  the  vessel  containing  the  alcohol 
and  at  the  same  time  exerts  a  considerable  pressure  upon 
it.  In  1877  Pfeffer  measured  this  pressure,  which  is  ex- 


PHYSICAL  CHEMISTRY  143 

hibited  also  between  water  and  an  aqueous  solution  or 
between  different  solutions,  and  de  Vries  showed  that 
solutions  could  be  prepared  which  exhibited  no  pressure 
when  thus  separated. 

Experiments  of  Van't  Hoff .  —  The  connection  between 
osmotic  pressure  and  the  facts  discovered  as  to  boiling 
and  freezing  points  and  vapor  pressure  was  worked  out 
in  the  latter  part  of  the  nineteenth  century  by  Van't 
Hoff,  who  also  made  a  thorough  investigation  of  the  phe- 
nomena of  osmotic  pressure.  He  found  in  the  course 
of  the  latter  investigation  that  when  a  substance  is  dis- 
solved in  a  liquid  the  molecules  exert  the  same  sort  of 
pressure  on  its  surface  as  they  would  if  they  existed  in 
the  form  of  a  gas  and  occupied  the  same  volume.  The 
bearing  of  the  molecular  weight  relations  then  is  evident. 
When  substances  are  taken  in  the  proportion  of  their 
molecular  weights  they  contain  the  same  number  of  mole- 
cules and  will  obey  the  gas  laws  as  to  pressure,  etc., 
provided  there  is  a  freedom  of  movement  similar  to  that 
in  a  gas  and  no  change  in  the  molecule. 

lonization  Theory.  —  Further  light  on  the  subject  came 
through  the  work  of  Arrhenius  on  electrolysis.  He 
reached  the  conclusion  that  in  a  solution  through  which 
a  current  is  passing  only  a  portion  of  the  particles  take 
part  in  the  conduction.  The  proportion  of  such  con- 
ducting particles  he  called  the  "activity  coefficient." 
This  activity  coefficient  was  found  to  be  proportional  to 
the  "affinity  coefficient"  of  Ostwald.  From  a  comparison 
of  these  facts  of  electrolysis  with  the  facts  above  men- 
tioned the  modern  theory  of  ionization  was  reached.  The 
various  compounds  are  divided  into  two  classes:  those 
which  conduct  electricity,  or  electrolytes,  and  those  which 


144  HISTORY  OF  CHEMISTRY 

do  not,  or  non-electrolytes.  The  electrolytes  vary  in 
their  conducting  power.  When  electrolytes  are  dissolved 
in  water  they  separate  or  ionize  into  two  ions,  one  posi- 
tively and  the  other  negatively  charged.  In  the  case 
of  complete  ionization  there  would,  therefore,  be  twice 
as  many  particles  present  as  there  were  molecules  origi- 
nally. This  is  approximately  the  case  when  strong  acids 
or  bases  are  the  electrolytes.  Twice  the  pressure  would, 
therefore,  be  exerted,  as  this  is  due  to  the  number  of  the 
particles  and  is  independent  of  their  nature.  Those 
which  do  not  electrolyze  show  no  change  in  the  number 
of  particles  and  hence  behave  normally.  The  strong 
support  of  the  ionization  theory  by  Ostwald  did  much 
to  bring  about  its  general  introduction.  It  has  served 
to  explain  many  reactions  which  were  before  difficult 
to  understand,  though  there  are  still  instances  which  pre- 
sent difficulties  in  the  way  of  its  application. 

Colloidal  Chemistry.  —  The  conceptions  introduced  by 
physical  chemistry  now  play  an  important  part  in  all 
branches  of  chemistry  and  are  essential  to  the  under- 
standing of  much  that  goes  on  both  in  experimental 
and  technical  work.  Among  other  things  it  has  been 
made  clear  that  besides  the  well-known  molecular  com- 
pounds with  definite  constitution  and  structure  there  are 
other  molecular  aggregations,  often  containing  hundreds 
of  atoms,  which  do  not  follow  the  fundamental  laws  of 
chemistry,  as,  for  instance,  the  law  of  definite  propor- 
tions, and  which  play  a  most  important  part  in  every- 
day life  and  in  the  industries.  These  are  grouped  as  col- 
loids and  form  a  distinct  division  of  the  science  under 
the  name  of  colloidal  chemistry.  The  first  work  upon 
these  substances  began  with  Graham's  diffusion  experi- 


PHYSICAL  CHEMISTRY  145 

ments  in  1850  in  which  he  found  that  by  means  of  dialysis 
substances  could  be  separated  into  crystalloids,  which 
form  real  solutions  and  diffuse  more  or  less  readily  through 
an  animal  membrane,  and  colloids,  which  do  not  diffuse 
at  all  or  only  very  slowly.  Some  colloids  are  apparently 
soluble  in  water,  but  it  has  been  proved  that  they  are  really 
present  in  a  state  of  very  fine  subdivision  and  are  only 
suspended  in  the  liquid.  A  very  large  number  of  sub- 
stances have  this  property  of  existing  as  colloids,  whether 
elements  or  compounds,  and  a  new  field  of  very  interesting 
and  complex  phenomena  has  been  opened  up.  Colloids 
form  what  are  called  adsorption  compounds  which  are 
more  or  less  stable  to  the  action  of  water.  In  these 
the  components  may  be  present  in  indefinite  proportions. 


CHAPTER    XVI 

BIOCHEMISTRY 

As  has  been  related,  the  old  man-erected  barrier  of  a 
hypothetical  vital  force  was  overthrown  and  organic 
chemistry  developed  into  that  branch  of  the  science 
which  embraced  the  largest  number  of  known  compounds, 
running  up  into  the  hundreds  of  thousands,  and  attracted 
most  of  the  investigators.  It  was  realized  that  life  proc- 
esses, as  they  are  still  called,  are  identified  with  physical 
and  chemical  changes  which  obey  the  ordinary  laws 
of  those  sciences  and  can  be  relied  upon  to  bring  about 
the  usual  results.  These  changes  are  definitely  subject 
to  the  influence  of  the  various  forms  of  energy  and  take 
place  normally  at  a  normal  temperature  and  under  a 
normal  pressure.  Under  changed  temperature  or  pressure 
they  take  an  abnormal  direction  or  velocity.  Many  of 
the  reactions  belong  to  the  reversible  class.  They  also 
obey  the  mass  law  and  are  affected  by  changes  of  con- 
centration. Until  these  facts  were  duly  recognized  the 
art  of  medicine  was  chiefly  on  an  empirical  basis  and  could 
not  be  called  a  science. 

The  complexity  of  the  molecules  involved,  many  being 
colloidal  in  nature,  and  the  diversity  of  the  possible 
changes  render  this  the  most  difficult  of  the  sciences 
to  master,  requiring  as  it  does  an  expert  knowledge  of 
physics,  chemistry,  and  physical  chemistry,  besides  other 
sciences.  Just  what  constitutes  life  remains  unknown. 

146 


BIOCHEMISTRY  147 

There  is  no  spontaneous  generation  or  autogenesis,  and 
life  processes  which  have  once  come  to  a  definite  end 
cannot  be  started  again,  though  some  of  the  minor  re- 
actions have  been  caused  to  repeat  themselves  under 
artificial  conditions.  So  there  is  in  a  way  a  life  barrier 
after  all,  but  not  one  which  forbids  the  reproduction 
of  substances  formed  in  plants  and  animals  and  which 
nullifies  the  laws  and  conceptions  of  the  sciences.  The 
field  is  open  for  intelligent  study  and  in  biochemistry  the 
chemist  finds  the  culmination  of  his  science. 

The  study  of  the  constituents  of  plants  and  animals 
and  especially  of  the  chemical  changes  taking  place 
among  them,  forms  the  branch  known  as  biochemistry. 
This  is  a  far  cry  from  the  ancillary  position  occupied 
by  the  science  in  its  earlier  periods.  The  term  physio- 
logical chemistry  covers  in  part  the  same  field  but  has 
a  more  limited  significance  in  so  far  as  chemistry  is  con- 
cerned. Of  course  the  examination  of  the  constituents 
of  organic  nature  did  not  escape  the  attention  of  those 
early  chemists  who  laid  the  foundations  of  modern  chem- 
istry. Fourcroy,  Vauquelin,  Chevreul,  Berzelius,  and 
others  contributed  investigations  along  these  lines. 
After  learning  the  composition  of  organs,  secretions,  etc., 
to  which  knowledge  many  chemists  contributed,  the 
next  step  was  to  find  out  the  conditions  under  which  these 
substances  were  formed,  their  relation  to  one  another, 
and  the  changes  they  underwent  —  in  other  words,  the 
reactions  going  on  in  the  body.  This  has  proved  a  far 
more  difficult  task.  A  vast  amount  of  work  remains  to 
be  done  along  these  lines.  Still  chemical  investigation 
has  rendered  great  service  in  clearing  up  much  that  was 
obscure  and  in  disproving  mistaken  conceptions  and 


148  HISTORY  OF  CHEMISTRY 

misleading  hypotheses.  The  number  of  these  investiga- 
tions is  far  too  great  to  be  detailed  here,  or  in  most  cases 
even  mentioned.  There  was  the  early  work  of  Mulder 
and  Liebig  and  others  on  the  proteins,  followed  many 
years  afterwards  by  the  epoch-making  researches  of  Emil 
Fischer  in  which  he  studied  their  hydrolysis  and  showed 
certain  of  them  to  be  made  up  of  amino-acids,  synthesized 
them,  and  revealed  the  products  of  their  hydrolysis. 
The  proteins  play  a  leading  part  in  the  life  processes 
and  a  knowledge  of  them  is  of  the  utmost  importance. 
They  still  form  probably  the  chief  point  of  attack  on 
the  part  of  chemists.  The  almost  endless  variety  of 
these  substances  tells  us  that  we  are  yet  far  from  fully 
understanding  their  composition  and  functions. 

Through  the  investigations  of  Chevreul  and  those 
who  followed  him  the  composition  of  the  fats  and  their 
hydrolytic  products  are  known.  Emil  Fischer  has  given 
a  deep  insight  into  the  constitution  of  the  sugars.  Starch 
and  other  carbohydrates  and  the  results  of  their  hydrol- 
ysis have  been  studied.  The  Schmidts,  Hoppe-Seyler, 
Nencki,  and  Ludwig  have  revealed  much  as  to  the  blood, 
its  composition  and  coagulation,  and  the  gases  carried. 
The  differences  between  venous  and  arterial  blood  have 
been  much  discussed  and,  in  fact,  satisfactorily  solved. 
The  researches  upon  inhaled  and  exhaled  air  and  the 
processes  taking  place  in  the  lungs  are  far  too  numerous 
to  recount;  and  so  also  with  regard  to  the  metabolism 
of  foods.  The  distinction  drawn  by  Buchner  in  1896 
between  fermentation  changes  caused  by  micro-organ- 
isms and  those  caused  by  enzymes  —  hydrolytic  changes 
brought  about  by  the  cell  itself  or  by  a  substance  secreted 
by  the  cell  but  acting  apart  from  it  —  was  of  import, 


BIOCHEMISTRY  149 

though  intracellular  action  must  be  taken  into  consid- 
eration and  the  mechanism  of  the  changes  is  not  yet 
definitely  understood. 

Of  the  many  other  contributors  to  the  development  of 
biochemistry  mention  may  be  made  of  Abderhalden, 
Atwater,  Lusk,  Chittenden,  Hammarsten,  and  Van 
Slyke.  The  field  is  too  large  to  dg  more. 


CHAPTER   XVII 
RADIOACTIVITY 

The  Discovery.  —  The  story  of  radioactivity,  this 
latest  and  crowning  marvel  in  scientific  discovery,  really 
begins  with  the  phenomena  in  the  tubes  which  were 
constructed  by  Crookes  in  1879  and  which  have  been 
named  after  him.  The  phenomena  observed  in  these 
high-vacuum  tubes  when  a  current  of  high  potential  was 
passed  through  them  led  Crookes  to  suggest  that  one 
might  be  dealing  with  a  fourth  state  of  matter,  which  was 
not  a  bad  guess  when  one  considers  the  revelations  which 
have  followed.  There  were  observed  streams  of  minute 
particles  which  could  be  deflected  by  a  magnet  and  so 
had  some  of  the  properties  of  matter.  These  proceeded 
in  straight  streams  through  perforations  in  the  anti- 
cathode.  There  were  also  contrary  streams  of  negative 
electrons,  and  later  Rontgen  found  that  by  use  of  the 
anti-cathode  very  penetrating  rays  were  obtained.  These 
were  after  the  order  of  light  and  easily  passed  through 
the  glass  walls  of  the  tubes.  They  affected  sensitive 
plates  and  photographs  could  be  taken  with  them.  He 
called  these  X-rays. 

As  these  phenomena  were  accompanied  by  phospho- 
rescence, Becquerel  conceived  the  idea  that  similar  photo- 
graphs might  be  taken  by  means  of  naturally  occurring 
phosphorescent  substances,  a  number  of  which  were 
known.  His  efforts  failed  with  all  phosphorescent  sub- 

150 


RADIOACTIVITY  151 

stances  known  to  him  until  he  tried  the  salts  of  uranium 
with  which  he  had  previously  done  some  experimental 
work  and  some  of  which  he  had  noticed  were  phospho- 
rescent. One  class  of  these  salts  is  phosphorescent, 
while  the  other  is  not,  but  he  found  that  both  classes 
gave  off  rays  that  acted  upon  the  sensitive  plates.  These 
new  unknown  rays  for  a  time,  therefore,  were  known  as 
Becquerel  rays.  Further  investigation  showed  that  all 
minerals  containing  uranium  showed  this  effect.  Ex- 
amination proved  that  the  intensity  of  the  activity  of  an 
uranium  compound  was  determined  solely  by  the  amount 
of  uranium  and  was  independent  of  the  other  elements 
present  with  which  it  might  be  combined.  It  was  accord- 
ingly a  property  of  the  uranium  atom  and  to  be  classed 
as  a  new  atomic  property.  Others  were  attracted  to 
this  search  and  it  was  found  that  only  one  other  element 
possessed  this  property  in  any  marked  degree  and  that 
was  thorium.  Rubidium  and  potassium  showed  very 
slight  and  partial  activity. 

Radium.  —  During  an  examination  of  other  uranium 
minerals  in  which  the  intensity  of  the  radiations  was 
measured  Madame  Curie  discovered  that  certain  of  them 
showed  a  much  greater  activity  than  could  be  ascribed 
to  the  amount  of  uranium  present.  From  this  she  con- 
cluded that  they  must  contain  some  unknown  element 
or  elements  which  were  more  radioactive.  Working 
with  very  large  quantities  of  material  and  in  a  most 
painstaking  and  laborious  manner,  she  found  that 
by  using  ordinary  laboratory  methods,  such  as  precipi- 
tation and  crystallization,  she  obtained  a  minute  residue 
which  was  intensely  radioactive.  One  such  residue  was 
obtained  when  bismuth  salts  were  used  as  the  reagent. 


152  HISTORY  OF  CHEMISTRY 

This  gave  spectroscopic  indications  of  the  presence  of 
a  new  element  which  she  named  polonium  but  which 
she  was  unable  to  isolate  completely.  When  barium  salts 
were  used  as  the  precipitating  reagent  she  obtained 
another  residue,  also  exceedingly  active.  From  this 
the  active  element  was  separated,  its  spectrum  mapped, 
and  its  atomic  weight,  valence,  and  other  properties 
determined.  To  this  she  gave  the  name  radium.  Two 
other  elements  have  been  detected  by  analogous  pro- 
cesses—  actinium  by  Debierne  and  ionium  by  Boltwood 
—  but  their  separation  in  a  pure  state  has  not  been 
accomplished. 

The  Radiations.  —  When  the  emanations  coming  from 
these  radioactive  substances  were  examined  by  the  ioni- 
zation  method  they  were  found  to  be  electrically  charged. 
By  means  of  the  electroscope  some  were  found  to  carry 
a  positive  and  some  a  negative  charge.  Their  power 
of  penetration,  as  tested  by  thin  sheets  of  metal,  etc., 
differed  greatly,  and  their  velocity  ranged  from  one-fif- 
teenth that  of  light  to  one  many  times  greater.  Also, 
by  examination  in  a  magnetic  field  it  was  found  that 
some  were  not  deflected,  some  slightly,  and  some  very 
greatly.  It  was  evident  that  the  radiations  were  com- 
posite and  made  up  of  different  kinds  of  rays.  Comparing 
the  results  noted  above,  three  classes  of  rays  were  dis- 
tinguished and  identified.  One  that  was  called  the  alpha 
ray  was  positively  charged,  was  slightly  deflected,  and  had 
a  low  penetration  but  the  greatest  power  of  ionization. 
It  had  the  least  velocity,  about  one-fifteenth  that  of 
light,  and  produced  scintillations  upon  a  zinc  sulphide 
screen.  This  was  identified  with  the  canal  rays  which 
had  been  observed  in  the  Crookes  tubes.  A  second, 


RADIOACTIVITY  153 

the  beta  ray,  was  negatively  charged  and  greatly  de- 
flected. It  had  an  ionizing  power  of  only  one  per  cent 
of  that  of  the  alpha  ray,  a  greater  penetrating  power, 
and  a  velocity  after  the  order  of  light.  This  was  identi- 
fied with  the  negative  electron.  The  third  variety  of 
ray  was  identified  with  the  X-ray.  It  was  not  charged 
electrically  nor  deflected  by  the  magnet,  had  only  the 
hundredth  of  a  per  cent  of  the  ionizing  power  of  the  alpha 
ray  and  by  far  the  greatest  penetrating  power.  Its 
velocity  was  found  to  be  after  the  same  order  as  that 
of  light.  In  other  words,  here  were  chemical  substances  — 
elements  —  which  gave  rise  to  the  same  phenomena  that 
had  been  observed  in  the  Crookes  tube. 

Radioactive  Substances.  —  It  was  soon  discovered 
that  radioactivity  could  be  induced  in  a  wire  or  sheet 
of  metal  suspended  over  a  radioactive  substance;  also 
that  the  radioactive  substance  could  be  separated  from 
a  solution  of  a  thorium  or  uranium  compound  by  the 
ordinary  chemical  operation  or  precipitation.  In  this 
it  showed  its  nature  or  behavior  to  be  similar  to  that  of 
the  ordinary  chemical  element  or  compound.  But  this 
additional  fact  was  noted.  When  in  the  solution  of  the 
uranium  salt,  for  instance,  the  radioactive  substance 
had  been  separated  by  precipitation  the  uranium  salt 
became  inactive  and  the  activity  was  transferred  to  the 
precipitate.  In  the  lapse  of  time,  however,  the  uranium 
regained  its  activity  and  the  precipitate  which  had  been 
removed  lost  it.  The  operation  could  be  repeated  as 
often  as  desired.  Some  process  was  going  on  in  which 
the  uranium  or  thorium  atoms  played  the  part  of  a  chem- 
ical factory  producing  continuously  hitherto  unknown  sub- 
stances. But  the  process  was  either  one  of  producing 


154  HISTORY  OF  CHEMISTRY 

something  out  of  nothing  or  generating  these  products 
out  of  their  own  substance. 

A  number  of  new  substances  were  obtained  in  this 
way,  were  separated,  examined,  and  found  to  be  them- 
selves sending  off  radiations  and  undergoing  changes. 
Some  lasted  only  a  very  short  while,  others  days  or 
years,  and  there  were  yet  others  whose  life  period  could 
only  be  calculated  in  terms  of  centuries  after  measuring 
the  rate  of  decay.  These  new  substances  were  distin- 
guished from  one  another  chiefly  by  their  duration 
value  and  by  the  character  of  their  emanations.  At  least 
three  of  these  are  gases  and  these  gases  are  monatomic 
and  belong  to  the  argon  group  in  the  Periodic  System. 
For  some  the  spectra  were  mapped  and  chemical  prop- 
erties, valence,  and  other  distinguishing  characteristics 
determined.  They  were  distinct  elements  with  the 
usual  elemental  physical  and  chemical  characteristics. 
Altogether  more  than  thirty  of  these  strange  new  ele- 
ments have  been  discovered  and  three  distinct  equi- 
librium series  determined. 

Disintegration  Theory.  —  Rutherford  proposed  as  an 
explanation  of  these  transformations  a  theory  of  dis- 
integration which  has  been  generally  accepted.  While 
there  have  been  many  workers  in  the  field  who  have 
rendered  valuable  service,  it  is  to  this  distinguished 
man,  who  combined  the  attainments  of  mathematician, 
physicist,  and  chemist  along  with  rare  insight  and  vision, 
that  science  is  chiefly  indebted  for  the  elucidation  of 
the  phenomena  of  radioactivity  and  the  resulting  clear- 
ing up  of  many  of  the  unsolved  problems  of  the  past. 

According  to  this  theory,  one  out  of  a  vast  number 
of  uranium  atoms  becomes  unstable  in  every  minute 


RADIOACTIVITY  155 

fraction  of  time  and  bursts  with  great  violence  for  so 
tiny  an  object,  expelling  one  or  two  alpha  particles  and 
forming  a  new  atom.  This  is  much  more  unstable  and 
breaks  up  after  a  shorter  interval,  losing  an  electron; 
and  so  there  is  a  series  of  transformations  in  which  alpha 
particles  and  electrons  are  expelled  and  the  great  energy 
transformed,  it  may  be,  into  the  gamma  or  X-rays. 
In  this  series  we  come  to  radium,  more  stable,  it  is  true, 
but  also  disintegrating.  Finally  an  end-product  seems 
to  be  reached  and  in  this  the  change  is  at  least  exceed- 
ingly slow,  though  it  is  still  radioactive.  This  end- 
element  is  so  similar  or  closely  akin  to  lead  that  it  can 
not  be  separated  from  it  and  is  called  radioactive  lead. 
Its  atomic  weight  has  been  most  carefully  determined 
by  Richards,  Honigschmid,  and  others  and  the  atomic 
weight  found  to  be  over  one-half  a  per  cent  less  than 
that  of  ordinary  lead.  In  the  same  way  the  thorium 
atom  breaks  up  and  there  is  formed  a  different  series 
in  which  the  rate  of  disintegration  is  different.  The 
end-product  again  is  a  radioactive  lead,  and  this  time 
the  atomic  weight  is  greater  than  that  of  lead.  It  has 
been  noted  that  in  uranium  and  thorium  minerals  there 
are  fairly  accordant  ratios  between  the  amount  of  the 
uranium  or  thorium  and  these  end-products,  indicating 
that  a  sort  of  equilibrium  has  been  reached. 

This  disintegration  is  entirely  beyond  outside  control. 
No  means  of  starting  or  stopping  it  is  known.  There 
would  seem  to  be  an  inherent  instability  in  these  the  two 
largest  of  the  atoms.  Neither  the  highest  nor  the  lowest 
temperatures  obtainable  have  any  effect  in  increasing 
or  retarding  the  velocity  of  change.  Furthermore,  the 
energy  freed  is  beyond  all  comparison  greater  than  that 


156  HISTORY  OF  CHEMISTRY 

from  any  other  known  source.  This  has  been  shown 
by  calorimetric  determinations. 

The  rays  emanating  from  a  substance  like  radium  are 
known  to  exert  a  profound  effect  upon  various  organic 
and  inorganic  substances,  the  molecules  of  compounds 
and  elements  undergoing  dissociation,  and  proof  has 
been  brought  forward  that  at  least  one  atom  —  that  of 
nitrogen  —  has  been  decomposed  when  subjected  to  the 
action  of  the  alpha  particles.  That  the  atom  of  one  ele- 
ment can  be  built  up  by  these  rays  has  been  clearly  shown 
by  a  remarkable  experiment  of  Rutherford.  In  this  ex- 
periment alpha  particles  coming  from  radium  emanations 
passed  through  thin  glass  walls  of  a  tube  into  a  surround- 
ing tube  with  thicker  walls  through  which  they  could 
not  pass.  This  outer  tube  had  been  carefully  evacuated, 
so  far  as  possible,  of  all  gas  before  the  beginning  of  the 
experiment.  A  sufficient  amount  of  the  alpha  particles 
had  entered  it  in  the  course  of  two  days  to  yield  a  dis- 
tinct spectrum  which  coincided  fully  with  the  spec- 
trum of  helium.  The  helium  atom,  therefore,  is  built 
up  of  alpha  particles  and  electrons  obtained  from  the 
glass  or  during  the  sparking  necessary  to  get  the  arc 
spectrum. 

Constitution  of  the  Atom.  —  Basing  his  conception  on 
this  experiment  and  on  the  disintegration  phenomena, 
Rutherford  announced  his  theory  as  to  the  constitu- 
tion of  the  atom.  In  this  the  atom  is  conceived  to  have 
a  nucleus  of  positive  electricity  surrounded  by  one  of 
negative  electricity  or,  to  express  it  a  little  differently, 
to  be  made  up  of  a  positive  nucleus  of  protons  and 
electrons  with  outer  envelopes  of  electrons  moving  in 
orbits.  This  theory  received  confirmation  from  the  facts 


RADIOACTIVITY  157 

discovered  in  connection  with  the  "recoil  atoms"  and 
the  "  stopping  power  "  exhibited  by  various  metals  and 
gases.  Rutherford's  atom  was  supposed  to  be  spherical. 
Cubical  atomic  models  have  also  been  suggested.  Bohr's 
model  and  that  of  Langmuir  differ  from  that  of  Ruther- 
f  o*rd  in  details  but  all  agree  as  to  the  atom  being  composed 
of  negative  and  positive  electricity.  It  is  interesting  to 
note  that  after  the  lapse  of  a  century  there  is  a  return 
to  the  suggestion  of  Davy  and  the  more  elaborated  con- 
ception of  Berzelius.  Changed  in  form  and  detail  and  am- 
plified through  greatly  increased  knowledge,  the  conception 
comes  back  with  a  firm  basis  of  experimental  evidence. 

The  New  Atom  and  its  Properties.  —  It  would  seem 
that  at  last  there  was  at  hand  an  explanation  of  such 
unsolved  problems  as  the  combining  power  and  the 
valence  of  the  atom  and  the  underlying  principle  of  the 
Periodic  System.  Soddy  and  others  have  done  much 
to  bring  the  new  facts  to  bear  upon  such  problems  as 
these.  Entire  agreement  has  not  been  reached  but  some 
results  can  be  given  without  going  into  details. 

In  the  first  place,  it  was  found  that  the  loss  of  an  alpha 
particle  reduced  the  atomic  weight  of  one  of  these  new 
elements  by  four,  which  is  the  atomic  weight  of  helium. 
At  the  same  time  the  atom  in  its  chemical  relations 
changed  two  groups  from  the  negative  to  the  positive 
side  in  the  Periodic  Table.  The  loss  of  a  beta  particle, 
or  electron,  caused  a  change  of  one  place  in  the  opposite 
direction,  involving  a  change  in  valence  and  combining 
power  or  affinity.  The  loss  of  two  electrons  neutralized 
the  loss  of  one  alpha  particle.  Noting  that  three  alpha 
particles  are  lost  from  uranium  to  radium,  the  atomic 
weight  of  radium  should  be  238  -  12  =  226,  which 


158  HISTORY  OF  CHEMISTRY 

agrees  with  the  actual  determinations.  So,  too,  the 
atomic  weight  of  the  radioactive  lead  has  been  calculated 
with  strong  confirmatory  experimental  evidence  from 
actual  determinations. 

In  ionization  there  is  an  exchange  of  electrons  between 
the  separating  ions.  When  a  current  is  passed  through 
a  solution  of  an  electrolyte  these  ions,  on  reaching  the 
electrodes,  regain  or  give  up  the  electron,  respectively, 
and  ordinary  atoms  result.  Again,  the  properties  of 
the  atoms  are  not  dependent  upon  nor  determined  by 
the  atomic  weights,  which  had  practically  been  recognized 
by  Mendeleeff  in  constructing  his  table,  though  he  laid 
down  as  a  fundamental  principle  that  the  properties 
were  functions  of  the  atomic  weights.  The  mass  or 
weight  is  just  one  of  the  properties  and  is  itself  deter- 
mined by  the  positive  nucleus.  The  properties  are  deter- 
mined by  the  electrical  relations  and  valence  is  changed 
by  the  loss  of  an  electron.  For  instance,  when  the  valence 
of  iron  or  copper  is  changed  the  atom  is  definitely  trans- 
ferred to  another  group,  a  process  which  can  readily  be 
reversed. 

So  a  new  conception  arises,  namely,  that  in  the  build- 
ing up  of  these  elements  there  is  a  definite  order  and 
that  in  the  series  each  has  an  assigned  place  correspond- 
ing to  a  number  which  is  now  called  the  atomic  number. 
This  number  can  be  determined  by  the  "stopping  power" 
of  the  element  hi  question,  that  is,  its  relative  penetra- 
bility. The  atomic  number  is  now  determined  more  con- 
veniently and  accurately  by  the  method  of  Moseley  in 
which  the  shifting  of  certain  lines  in  the  X-ray  spectra  of 
the  elements  is  mapped  and  their  order  definitely  settled. 

Factors  in  Element  Formation.  —  It  is  manifest  that 


RADIOACTIVITY  159 

given  certain  factors  of  balanced  electrical  relations  it 
would  not  be  difficult  to  construct  a  series  such  as  that 
which  is  found  in  the  known  elements  presenting  numer- 
ical regularities  as  to  their  atomic  weights.  It  was  this 
that  Cooke  and  Dumas  attempted  to  do  in  the  middle 
of  the  nineteenth  century,  though  they  were  of  course 
in  ignorance  as  to  the  bearing  that  electricity  might  have 
in  the  matter.  A  number  of  chemists  and  physicists 
of  the  day  have  been  engaged  in  this  task  since  the 
Rutherford  atom  was  recognized.  The  work  is  neces- 
sarily in  the  tentative  stage  as  yet.  The  factors  usually 
taken  are  helium  and  hydrogen,  as  suggested  by  Harkins, 
though  others  have  been  suggested.  As  Rutherford  has 
pointed  out,  helium  is  a  secondary  structure  and  itself 
made  up  of  four  hydrogens. 

Isotopes.  —  In  attempting  to  place  the  radioactive  ele- 
ments in  their  proper  positions  in  the  Periodic  Table 
Soddy  found  that  when  they  were  classified  according, 
to  their  properties  and  the  losses  of  alpha  particles  and 
electrons  sustained,  several  closely  analogous  elements 
would  fall  in  the  same  space,  though  their  atomic  weights 
might  be  widely  different.  Thus  there  are  nine  isotopes 
of  lead  with  the  atomic  number  82.  This  name  isotope 
was  suggested  by  Soddy  to  designate  an  element  which 
is  so  closely  analogous  to  one  of  the  known  elements  that 
it  is  chemically  inseparable.  The  difference  lies  in  certain 
physical  properties,  notably  the  atomic  weight.  It  has 
been  suggested  that  certain  of  the  rare  earths  which 
have  presented  great  difficulties  in  the  way  of  their 
proper  placing  in  the  Table  are  also  isotopes. 

Another  recent  development  in  this  matter  of  isotopes 
is  that  some  of  the  well-known  elements,  such  as  neon, 


160  HISTORY  OF  CHEMISTRY 

chlorine,  hydrogen,  etc.,  can  by  physical  methods,  mainly 
diffusion  experiments,  be  separated  into  portions  which 
exhibit  all  of  the  chemical  properties  of  the  element 
but  have  distinctly  differing  atomic  weights.  It  is  prob- 
ably true  then  that  in  determining  the  atomic  weight 
of  an  element  the  final  result  is  an  average  of  the  weights 
of  the  atoms  present. 

Recent  methods  devised  by  J.  J.  Thomson  and  Aston 
have  made  it  possible  to  determine  the  number  of  iso- 
topes of  an  element,  their  relative  proportion  with  an 
accuracy  of  10-20  per  cent,  and  their  masses  or  atomic 
weights  with  great  accuracy.  These  methods  can  be 
applied  to  the  determination  of  the  atomic  weights  of  the 
known  elements  and  exceed  in  accuracy  the  best  chemical 
determinations.  By  this  means  it  has  been  shown  that 
atomic  weights  are  whple  numbers  when  referred  to  the 
standard  oxygen  as  sixteen.  This  is  true  up  to  and  includ- 
ing chlorine  and  probably  will  be  found  true  of  the  others. 
In  the  case  of  hydrogen  the  atomic  weight  1.008  obtained 
by  chemical  methods  is  confirmed. 

The  nucleus,  therefore,  is  made  up  of  alpha  particles 
called  protons  and  of  electrons.  According  to  Aston,  it 
is  electrically  neutral.  This  is  called  the  electrical  con- 
tent and  decides  the  atomic  weight  of  the  element  and 
its  position  in  the  Periodic  System.  The  surrounding 
electrons  in  their  orbits  decide  the  valence  and  the 
chemical  characteristics.  The  term  isobars  has  been 
adopted  for  such  elements  as  have  the  same  atomic  weight 
but  differ  in  chemical  characteristics,  while  an  isotope 
is  one  which  has  the  same  chemical  characteristics  but 
different  atomic  weight. 

It  is  suggested  that  the  term  atomic  weight  be  used 


RADIOACTIVITY  161 

for  the  average  weight  of  the  element  as  accompanied  by 
its  isotopic  companions  and  that  atomic  mass  be  used 
for  the  weights  of  the  individual  element  and  its  isotopes. 

Matter  and  the  Universe.  —  The  impression  left  after 
all  of  this  is  one  of  instability  and  change  constantly  going 
on,  not  merely  in  the  visible  objects  around  us  and  in 
their  components  but  in  the  very  atoms  themselves. 
If  these,  which  were  once  called  simple  bodies  and  then 
atoms  are  proved  to  be  unstable,  the  question  of  stability 
has  merely  been  pushed  one  step  farther  and  we  reach 
the  electrically  charged  units  or  the  individual  electric 
charges  and  adopt  the  more  recent  term  electron. 
Mutability  drove  some  of  the  early  Greek  philosophers 
to  despair  and  an  abandonment  of  the  search.  But 
man  has  grown  in  many  ways  into  a  higher  being  and  the 
very  difficulties  that  would  thwart  him  are  but  an  in- 
centive to  all  that  is  finest  and  highest  in  him. 

To  show  how  far  it  is  possible  to  peer  into  the  invis- 
ible and  the  minuteness  of  detail  to  which  the  search 
has  been  pushed,  it  is  well  to  close  this  account  by  citing 
certain  figures  given  by  Rutherford  and  confirmed  by 
independent  investigators  as  J.  J.  Thomson  and  others: 

Charge  carried  by  the  hydrogen  atom,  4.65  X  10~10  electro- 
static units. 

Charge  carried  by  the  alpha  particle,  9.3  X  10~10e.s. 
Number  of  atoms  in  1  gram  hydrogen,  6.2  X  1023. 
Mass  of  an  atom  of  hydrogen,  1.6  X  10"24  gram. 
Number  of  molecules  per  cc.  any  gas,  2.78  X  1019. 


INDEX 


PAGE 

Abderhalden 149 

Acids 22 

Acid  theory,  Lavoisier's.  .       51 

Acid  theory,  new 104 

Acids,  polybasic 96 

Activity  coefficient 143 

Aetherin  theory 122 

Affinity 90,  91,  92 

Affinity,  strength  of 91,  93 

Affinity  tables 33,  44,  91 

Affinity,  views  as  to 43 

Agricola 27 

Air,  composition  of,  35, 39,  40,  46 
Air,  experiments  on  .  .31,  50,  61 

Albertus  Magnus 24 

Alcohol 25 

Alkalis 22 

Alkalis,  decomposition  of .     101 

Alkalizing  principle 105 

Amines,  discovery  of 130 

Ammonium  chloride 22 

Ampere 69 

Analysis 38 

Anaxagoras 16 

Anaximenes 13 

Apparatus 18 

Aqua  regia 22 

Arabians 19,  20 

Archelaus..  13 


PAGE 

Arfvedson Ill 

Aristotle 17 

Arrhenius 140,  143 

Arsenic  sulphides 5 

Ascending  series  of  Glad- 
stone         84 

Aston 159,  160 

Atmosphere 49,  57 

Atom,  composite 87 

Atom,  constitution  of . .  155,  160 
Atom,  disintegration  of . . .     153 

Atom,  nature  of 81,  82,  92 

Atoms 14,  62 

Atoms,  recoil 156 

Atomic  attractive  force ...       90 

Atomic  chains 98 

Atomic  models 156 

Atomicity 96 

Atomic  theory. . .  14,  15,  60,  126 

Atomic  weights 65,  70,  108 

Atomic  weights,  constancy 

of 78 

Atomic  weights,  Dalton's 

rules 66 

Atomic  weights,  Dumas  on     74 
Atomic  weights,  Gmelin's 

views 76 

Atomic  'weights,    numeri- 
cal relations ..  83 


163 


164 


INDEX 


PAGE 

Atomic  weights,  revision 
of 77 

Atomic  weights,  standard 
for 71 

Avogadro's  theory 69 

Bacon,  Francis 30 

Bacon,  Roger 24 

Baeyer 137 

Becquerel 149 

Benzene  theory 132 

Benzoic  acid  radical 122 

Bergman 38,  92 

Berthelot 140 

BerthoUet.  .42,  43,  63,  92,  103, 

138,  140 

Berzelius  73,  103,  106,  107,  108, 
110,  116,  117,  118,  120,  123, 

129,  147 

Biochemistry 146 

Black,  Joseph 55 

Blayden 142 

Boerhaave 42,  91 

Bohr 89,  156 

Boltwood 151 

Boyle,  Robert 30 

Bragg 134 

Bricks 6 

Bronze 4 

Buchner 148 

Bunsen Ill 

Bussy Ill 

I 

Cannizzaro 78 

Carbon,  valence  of 98 

Carius 120 

Carlisle..  100 


PAGE 

Cavendish 37,  112 

Cement 5 

deChancourtois 84 

Chemistry,  beginnings  of.  1 

Chevreul 116,  119,  147 

Chittenden 149 

Glaus Ill 

Clausius 141 

Coal  tar  syntheses 136 

Colloidal  chemistry 144 

Colors 6 

Combustion,  chemistry  of  34 
Combustion,  Lavoisier's 

experiments 45 

Combustion,  theory  of .  .  .  36 
Combustion,  views  of 

Priestley 58 

Compounds 33,  38 

Compound  radicals 124 

Constant  proportions,  law 

of 63 

Cooke 158 

Courtois 104 

Copper 3 

Copper  oxides 5 

Cowper 132 

Crookes 79,  149 

Curie,  Madame 150 

Dark  Ages 19 

Davy 100,  105 

Davy's  atoms 92 

Debierne 151 

DeVille 77 

Disintegration  theory ....     153 

Dobereiner 83,  120 

Dualism  overthrown 126 


INDEX 


165 


PAGE 

Dualistic  theory 110 

Dulong 72 

Dumas  ....74,  75,  95,  121,  124, 
126,  127,  130,  158 

Dyeing.. 6 

Electro-chemical  theory .  .  121 

Electrolytes 143 

Electrolytic  dissociation  . .  140 

Electrum 8 

Elements 14,38 

Elements,  additional Ill 

Elements,  complex 88 

Elements,  definition  of  ...  52 

Elements,  formation  of ...  156 
Elements,  interrelated. . .  .87,  88 

Empedokles   14 

Epicurus 17 

Equivalents,  electro-chem- 
ical   74 

Equivalents,  Wollaston's  .  72 

Erdmann 77 

Ether 15 

Evolution  of  science 1 

Faraday 74,  118,  140 

Faraday's  law 74 

Favre 93 

Fischer,  Emil 148 

Fourcroy 147 

Frankland 78,95,98 

Gases 28 

Gases,  diffusion  of 61 

Gases,  mixtures  of 60 

Gases,  monatomic 86,  112 

Gay-Lussac      67,  103,  104,  117, 

130 

Geber. .  21 


PAQE 

Geoffrey 91 

Gerhardt 129,  131 

Gibbs,  WiUard 140 

Gladstone 84,  88 

Glass 6 

Glass  apparatus 22 

Glauber 28,29,91 

Gmelin 76,83 

Gold 2 

Gold  purification 3 

Graebe 136 

Graham 95,  144 

Graphic  formulas 132 

Griess 136 

Guldberg 140 

Gunpowder 25 

Hammarsten 149 

Harkins 160 

Heat,  nature  of 50 

Heat  of  reactions 93 

Herakleitos 13 

Hermes 9,  10 

Hess 93 

Hippocrates 90 

Hittorf 141 

Hofmann 120,  136 

Homologous  series 130 

Hooke 36 

Hydrogen,  discovery  of ...  48 

Industrial  arts 2 

Industrial          chemistry, 

growth  of 99,  114 

lonization  theory 143 

Iron 3,  4 

Isomerism. .  117 


166 


INDEX 


PAGE 

Isomorphism 73 

Isotopes 80,  158,  159 

Kekule* 89,  131,  132,  133 

Kekule*  on  valence  of  car- 
bon   98 

Kirchoff 139 

Klaproth 99 

Kohlrausch 141 

Kolbe 98 

Landolt 79 

Langmuir 89,  157 

Langmuir's  model  atom . .     156 

Laplace 93 

Laue 134 

Laurent 95,  128,  129 

Lavoisier  36,  37,  44,  93,  115,  120 

Laws 11 

Lead 3,5 

Lead,  white 5 

Leather 6 

Lennsen 83 

Liebermann 137 

Liebig  96,   118,  120,  123,   124, 
127,  148 

Lime 5 

Lockyer 113 

Ludwig 148 

Lusk 149 

Manganese  dioxide 5 

Manuscripts 10,  11 

Marchand 77 

Marignac 77 

Mass  action 139,  140 


PAGE 

Matter  and  universe 159 

Matter,  nature  of 32,  50 

Medicaments 7 

Mendeleeff 84 

Mercury 2 

Metallurgy 2 

Metals 2 

Metals,  transmutation  of,  20,  21 

Meyer,  Lothar 84 

Meyer,  Victor 120 

Middle  Ages 24 

Mitscherlich 73 

Model  atoms 156 

Monatomic  gases. .  .86,  113,  154 

Moore 114 

Mosander Ill 

Moseley 87 

Mordants 6 

Mulder 148 

Multiple  proportions,  law 

of 64 

Muriatic  acid 103 

Mutability  of  nature,  11,  12, 161 
Mysticism 9 

Naming  the  science 8 

Nature  of  the  atom 81,  157 

Nencki 148 

New  chemistry,  bases  of . .  59 
New    chemistry,    founda- 
tions of 48 

New  elements 99 

Newlands 84 

Nicholson 100 

Nitric  acid 22 

Nollet 142 

Nucleus  theory 129 


INDEX 


167 


PAGE 

Octaves,  law  of 84 

Odling 83,  95 

Organic  analysis 120 

Organic  chemistry,  devel- 
opment of 115 

Organic  substances,   clas- 
sification    120 

Organic    substances,    La- 
voisier on 51 

Organo-metallic       com- 
pounds   95 

Osmotic  pressure 142 

Ostwald 143,  144 

Oxygen,  discovery  of 36,  56 

Paints 6 

Paracelsus 26 

Pasteur 134 

Periodic  system 84 

Perkin 136 

Petit 72 

Pettenkofer 130 

Pfeffer 142 

Pharmacy 26 

Phase  rule 140 

Pherekides 13 

Phlogiston 35 

Phlogiston,    non-existence 

of 34 

Phlogiston  theory 34 

Photo-chemical  induction.  139 

Physical  chemistry 138 

Physiological  chemistry . .  146 

Polariscope 139 

Polyatomicity 96 

Pottery 6 

Priestley 36,37,56 


PAGE 

Proportions,  law  of  defi- 
nite        42 

Proust 63,  99 

Prout's  hypothesis 81 

Radiations 152 

Radical  theory 121,  122 

Radioactive  substances . . .     153 

Radioactivity 149 

Radioactivity    and    peri- 
odic system 156 

Radioactivity,      contribu- 
tions from 86 

Radioactivity,  induced .  . .     152 

Radium 151 

Ramsay 86,  113,  114 

Raoult 142 

Rayleigh 113 

Rays,  action  of 155 

Remsen 94 

Remsen    on    relation    of 

elements 87 

Replacement  value 95,  96 

Richter 60 

Rontgen 150 

Rutherford,  89, 154, 156, 159, 161 

Salt 5 

Saltpeter 5 

Saturation  capacity 96 

Scheele 39,  40,  41,  103,  119 

Scheerer 77 

Schmidt 148 

Schiitzenberger 79 

Science,  evolution  of 1 

Sefstrom Ill 

Silbermann..  93 


168 


INDEX 


Silver. 


PAGE 

3 

7 

Soddy 86,  157,  159 

Solutions,  properties  of . . .  141 

Specific  heats,  law  of 72 

Spectroscope Ill,  139 

Stas 77 

Stereochemistry 133 

Stromeyer Ill 

Structure,  theories  as  to . .  126 

Substitution  theory 126 

Sulphur 7 

Sulphuric  acid 22 

Symbols 109 

Tanning 6 

Telluric  screw 84 

Thales 13 

Th&iard 103 

Theories 12 

Theory,  rise  of 30 

Thermochemistry 93 

Thomsen 93 

Thomson 77 

Thomson,  J.  J 160,  161 

Tin 3,4 

Tinctures 27 

Toth 9 

Transmutation      of      ele- 
ments  20,  21 

Travers 114 

Triads 83 

Trichloracetic  acid 127 

Turner..  82 


PAGE 

Type  theory 129 

Unitary  theory 128 

Universe  and  matter 159 

Urea,  synthesis  of 118 

Valence. . .  .94,  97,  131,  156,  157 

Valence,  evolution  of 94 

van  Helmont 27 

van  Slyke 149 

van'tHoff 134,  143 

Vapor  densities 75 

Vauquelin 147 

Vinegar 5 

Vogel 79 

Volumes,  law  of 67,  68 

Waage 140 

Water,  composition  of 48 

Water,  transmutation  of . .       49 

Wilhelmy 140 

Williamson 95,  96,  130,  141 

Wohler Ill,  118,  119,  127 

Wollaston 72 

Wood 11 

World  building 16 

Wurtz 96 

Wurtz,  study  of  amines. .       97 

X-rays 150,153,155 

X-ray  spectra 87 

Zero  group 86,  112,113 

Zinc 3 

Zosimus i       18 


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